Method for determining precoding matrix indicator, user equipment, and base station

ABSTRACT

The present disclosure relates to methods for determining a precoding matrix indicator, user equipment, and base stations. One example method includes sending a first reference signal set to user equipment, where the first reference signal set is associated with a user equipment-specific matrix set, and receiving a precoding matrix indicator (PMI) sent by the user equipment, where the PMI is used for indicating a precoding matrix that is selected based on the first reference signal set by the user equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/697,789, filed on Nov. 27, 2019, which is a continuation of U.S.patent application Ser. No. 16/233,444, filed on Dec. 27, 2018, now U.S.Pat. No. 10,523,291, which is a continuation of U.S. patent applicationSer. No. 16/107,653, filed on Aug. 21, 2018, now U.S. Pat. No.10,263,674, which is a continuation of U.S. patent application Ser. No.15/950,820, filed on Apr. 11, 2018, now U.S. Pat. No. 10,141,990, whichis a continuation of U.S. patent application Ser. No. 14/936,092, filedon Nov. 9, 2015, now U.S. Pat. No. 9,967,008, which is a continuation ofInternational Application No. PCT/CN2013/075486, filed on May 10, 2013.All of the aforementioned patent applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of wirelesscommunications, and in particular, to a method for determining aprecoding matrix indicator, user equipment, and a base station.

BACKGROUND

By using a transmit beam forming (BF) or precoding technique and byusing a receive signal combination technology, a multiple input multipleoutput (MIMO) wireless system can obtain diversity and array gains. Atypical system that uses BF or precoding may usually be represented as:

y=HVs+n

where y is a received signal vector, H is a channel matrix, v is aprecoding matrix, s is a transmitted symbol vector, and n is measurednoise. Optimal precoding usually requires that a transmitter knows theentire channel state information (CSI). In a common method, userequipment quantizes instantaneous CSI and feeds back the instantaneousCSI to a base station. CSI information fed back by an existing LTE R8system includes a rank indicator (RI), a precoding matrix indicator(PMI), a channel quality indicator (CQI), and the like, where the RI andthe PMI indicate respectively a quantity of used layers and a usedprecoding matrix. A set of used precoding matrices is generally referredto as a codebook (sometimes each precoding matrix in the set is referredto as a code word). An existing Long Term Evolution (LTE) R8 4-antennacodebook is designed based on Householder transformation, and an R10system further introduces double-codebook design for 8-antenna. Theforegoing two codebooks are mainly for antenna design of a common basestation. A common base station uses a fixed or remote electrical tiltdowntilt to control a beam direction of an antenna in a verticaldirection, and a beam direction of the antenna may be adjusteddynamically through precoding or beam forming only in a horizontaldirection.

To reduce system costs and to achieve a higher system capacity andcoverage requirement at the same time, an active antenna system (AAS)has been widely deployed in practice. For the currently launched LTE R12standard, enhancement of communication performance after the AAS systemis introduced is considered. Compared with a conventional base stationantenna, the AAS further provides design flexibility in a verticaldirection, and meanwhile, for convenience of deployment, antenna portsin the AAS may be further increased. For example, a quantity of antennaports included in the current LTE R12 and future evolved versions may be8, 16, 32, 64, or even larger. A new requirement for codebook design,especially in aspects such as precoding performance, feedback overheadcompromise, and air interface support, is proposed. In such abackground, a new design solution for an AAS base station antenna, andespecially for a precoding matrix and a feedback process of the AAS basestation antenna, needs to be proposed.

SUMMARY

Embodiments of the present invention provide a method for determining aprecoding matrix indicator, user equipment, and a base station, whichcan improve CSI feedback precision without excessively increasingfeedback overhead, thereby improving system performance.

According to a first aspect, a method for determining a precoding matrixindicator is provided, including: receiving a first reference signal setsent by a base station, where the first reference signal set isassociated with a user equipment-specific matrix or matrix set;selecting a precoding matrix based on the first reference signal set,where the precoding matrix is a function of the user equipment-specificmatrix or matrix set; and sending a precoding matrix indicator PMI tothe base station, where the PMI corresponds to the selected precodingmatrix.

With reference to the first aspect and the foregoing implementationmanner of the first aspect, in a first implementation manner of thefirst aspect, the user equipment-specific matrix or matrix set isnotified by the base station to user equipment.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a second implementation manner of thefirst aspect, the first reference signal set includes one or morereference signal subsets, and the reference signal subset corresponds toa co-polarized antenna port subset, or corresponds to an antenna portsubset that is arranged in a same direction in an antenna port array, orcorresponds to an antenna port subset that is located at aquasi-co-location.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a third implementation manner of thefirst aspect, that the precoding matrix is a function of the userequipment-specific matrix or matrix set includes that: the precodingmatrix w is a product of two matrices W₁ and W₂, W=W₁W₂, where thematrix W₁ is a block diagonal matrix, the block diagonal matrix includesat least one block matrix, and each block matrix is a function of theuser equipment-specific matrix or matrix set.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a fourth implementation manner of thefirst aspect, each block matrix X is a Kronecker product of two matricesC and D , X=C⊗D, and at least one matrix in the two matrices C and D isa function of the user equipment-specific matrix or matrix set.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a fifth implementation manner of thefirst aspect, that at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set includesthat:

a k^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a _(m)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(D) , . . . ,e ^(jθ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shifts.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a sixth implementation manner of thefirst aspect, that a matrix in the user equipment-specific matrix ormatrix set is a matrix formed by columns being discrete Fouriertransformation DFT vectors, or a matrix formed by column vectors of aHadamard matrix or a Householder matrix.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a seventh implementation manner of thefirst aspect, that columns of the matrix in the user equipment-specificmatrix or matrix set are discrete Fourier transformation DFT vectorsincludes that: the DFT vector a_(l) satisfies:

${a_{l} = \begin{bmatrix}e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}} & e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}} & \ldots & e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}\end{bmatrix}^{T}},$

where []^(T) is a matrix transpose, M and N are positive integers, andN_(C)≥N or N_(D)≥N.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in an eighth implementation manner of thefirst aspect, with reference to the first aspect and the foregoingimplementation manners of the first aspect, in a sixth implementationmanner of the first aspect, the first reference signal set includes atleast one reference signal subset, and the reference signal subset isassociated with a set of the matrix C or the matrix D.

With reference to the first aspect and the foregoing implementationmanners of the first aspect, in a ninth implementation manner of thefirst aspect, the reference signal subset has a sending period longerthan that of another reference signal.

According to a second aspect, a method for determining a precodingmatrix indicator is provided, including: sending a first referencesignal set to user equipment, where the first reference signal set isassociated with a user equipment-specific matrix or matrix set; andreceiving a precoding matrix indicator PMI sent by the user equipment,where the PMI is used for indicating a precoding matrix that is selectedbased on the first reference signal set by the user equipment, and theprecoding matrix is a function of the user equipment-specific matrix ormatrix set.

With reference to the second aspect and the foregoing implementationmanner of the second aspect, in a first implementation manner of thesecond aspect, the user equipment-specific matrix or matrix set isnotified by a base station to the user equipment.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a second implementation manner of thesecond aspect, the first reference signal set includes one or morereference signal subsets, and the reference signal subset corresponds toa co-polarized antenna port subset, or corresponds to an antenna portsubset that is arranged in a same direction in an antenna port array, orcorresponds to a quasi-co-location antenna port subset.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a third implementation manner of thesecond aspect, that the precoding matrix is a function of the userequipment-specific matrix or matrix set includes that: the precodingmatrix w is a product of two matrices W₁ and W₂, W=W₁W₂, where thematrix W₁ is a block diagonal matrix, the block diagonal matrix includesat least one block matrix, and each block matrix is a function of amatrix in the user equipment-specific matrix or matrix set.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a fourth implementation manner of thesecond aspect, each block matrix X is a Kronecker product of twomatrices C and D , X=C⊗D, and at least one matrix in the two matrices Cand D is a function of the user equipment-specific matrix or matrix set.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a fifth implementation manner of thesecond aspect, that at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set includesthat:

a k^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ^(□) ,e ^(jθ) ^(□) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) ^(□) e^(j2π(N) ^(V) ^(/2−1)/N) ^(C) }a _(m)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a _(m)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shifts.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a sixth implementation manner of thesecond aspect, a matrix in a subset of the user equipment-specificmatrix or matrix set is a matrix formed by columns being discreteFourier transformation DFT vectors, or a matrix formed by column vectorsof a Hadamard matrix or a Householder matrix.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a seventh implementation manner of thesecond aspect, that columns of the matrix in the subset of the userequipment-specific matrix or matrix set are discrete Fouriertransformation DFT vectors includes that: the DFT vector a_(l)satisfies:

${a_{l} = \begin{bmatrix}e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}} & e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}} & \ldots & e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}\end{bmatrix}^{T}},$

where []^(T) is a matrix transpose, M and N are positive integers, andN_(C)≥N or N_(D)≥N.

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in an eighth implementation manner of thesecond aspect, the first reference signal set includes at least onereference signal subset, and the reference signal subset is associatedwith a set of the matrix C or the matrix D .

With reference to the second aspect and the foregoing implementationmanners of the second aspect, in a ninth implementation manner of thesecond aspect, the reference signal subset has a sending period longerthan that of another reference signal.

According to a third aspect, user equipment is provided, including: areceiving unit, configured to receive a first reference signal set sentby a base station, where the first reference signal set is associatedwith a user equipment-specific matrix or matrix set; a determining unit,configured to select a precoding matrix based on the first referencesignal set, where the precoding matrix is a function of the userequipment-specific matrix or matrix set; and a sending unit, configuredto send a precoding matrix indicator PMI to the base station, where thePMI corresponds to the selected precoding matrix.

With reference to the third aspect and the foregoing implementationmanner of the third aspect, in a first implementation manner of thethird aspect, the receiving unit is further configured to receive theuser equipment-specific matrix or matrix set notified by the basestation.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a second implementation manner of thethird aspect, the first reference signal set includes one or morereference signal subsets, and the reference signal subset corresponds toa co-polarized antenna port subset, or corresponds to an antenna portsubset that is arranged in a same direction in an antenna port array, orcorresponds to an antenna port subset that is located at aquasi-co-location.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a third implementation manner of thethird aspect, the precoding matrix W is a product of two matrices W₁ andW₂, W=W₁W₂ where the matrix W₁ is a block diagonal matrix, the blockdiagonal matrix includes at least one block matrix, and each blockmatrix is a function of the user equipment-specific matrix or matrixset.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a fourth implementation manner of thethird aspect, each block matrix X is a Kronecker product of two matricesc and D, X=C⊗D, and at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a fifth implementation manner of thethird aspect, that at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set includes:

a k^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a _(m)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shifts.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a sixth implementation manner of thethird aspect, a matrix in a subset of the user equipment-specific matrixor matrix set is a matrix formed by columns being discrete Fouriertransformation DFT vectors, or a matrix formed by column vectors of aHadamard matrix or a Householder matrix.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a seventh implementation manner of thethird aspect, the DFT vector a_(l) satisfies:

${a_{l} = \begin{bmatrix}e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}} & e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}} & \ldots & e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}\end{bmatrix}^{T}},$

where []^(T) is a matrix transpose, M and N are positive integers, andN_(C)≥N or N_(D)≥N.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in an eighth implementation manner of thethird aspect, the first reference signal set includes at least onereference signal subset, and the reference signal subset is associatedwith a set of the matrix C or the matrix D.

With reference to the third aspect and the foregoing implementationmanners of the third aspect, in a ninth implementation manner of thethird aspect, the reference signal subset has a sending period longerthan that of another reference signal.

According to a fourth aspect, a base station is provided, including: asending unit, configured to send a first reference signal set to userequipment, where the first reference signal set is associated with auser equipment-specific matrix or matrix set; and a receiving unit,configured to receive a precoding matrix indicator PMI sent by the userequipment, where the PMI is used for indicating a precoding matrix thatis selected based on the first reference signal set by the userequipment, and the precoding matrix is a function of the userequipment-specific matrix or matrix set.

With reference to the fourth aspect and the foregoing implementationmanner of the fourth aspect, in a first implementation manner of thefourth aspect, the sending unit is further configured to notify the userequipment of the user equipment-specific matrix or matrix set.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a second implementation manner of thefourth aspect, the first reference signal set includes one or morereference signal subsets, and the reference signal subset corresponds toa co-polarized antenna port subset, or corresponds to an antenna portsubset that is arranged in a same direction in an antenna port array, orcorresponds to a quasi-co-location antenna port subset.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a third implementation manner of thefourth aspect, the precoding matrix w is a product of two matrices W₁and W₂, W=W₁W₂ where the matrix W₁ is a block diagonal matrix, the blockdiagonal matrix includes at least one block matrix, and each blockmatrix is a function of the user equipment-specific matrix or matrixset.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a fourth implementation manner of thefourth aspect, each block matrix X is a Kronecker product of twomatrices C and D , X=C⊗D, and at least one matrix in the two matrices Cand D is a function of the user equipment-specific matrix or matrix set.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a fifth implementation manner of thefourth aspect, that at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set includesthat:

a k^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a _(m)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shifts.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a sixth implementation manner of thefourth aspect, a matrix in the user equipment-specific matrix or matrixset is a matrix formed by columns being discrete Fourier transformationDFT vectors, or a matrix formed by column vectors of a Hadamard matrixor a Householder matrix.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a seventh implementation manner of thefourth aspect, that columns of the matrix in the user equipment-specificmatrix or matrix set are discrete Fourier transformation DFT vectorsincludes that: the DFT vector a_(l) satisfies:

${a_{l} = \begin{bmatrix}e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}} & e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}} & \ldots & e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}\end{bmatrix}^{T}},$

where []^(T) is a matrix transpose, M and N are positive integers, andN_(C)≥N or N_(D)≥N.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in an eighth implementation manner of thefourth aspect, the first reference signal set includes at least onereference signal subset, and the reference signal subset is associatedwith a set of the matrix C or the matrix D.

With reference to the fourth aspect and the foregoing implementationmanners of the fourth aspect, in a ninth implementation manner of thefourth aspect, the reference signal subset has a sending period longerthan that of another reference signal.

According to a fifth aspect, user equipment is provided, including: areceiver, configured to receive a first reference signal set sent by abase station, where the first reference signal set is associated with auser equipment-specific matrix or matrix set; a processor, configured toselect a precoding matrix based on the first reference signal set, wherethe precoding matrix is a function of the user equipment-specific matrixor matrix set; and a transmitter, configured to send a precoding matrixindicator PMI to the base station, where the PMI corresponds to theselected precoding matrix.

With reference to the fifth aspect and the foregoing implementationmanner of the fifth aspect, in a first implementation manner of thefifth aspect, the receiver is further configured to receive the userequipment-specific matrix or matrix set notified by the base station.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a second implementation manner of thefifth aspect, the first reference signal set includes one or morereference signal subsets, and the reference signal subset corresponds toa co-polarized antenna port subset, or corresponds to an antenna portsubset that is arranged in a same direction in an antenna port array, orcorresponds to an antenna port subset that is located at aquasi-co-location.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a third implementation manner of thefifth aspect, the precoding matrix W is a product of two matrices W₁ andW₂, W=W₁W₂, where the matrix W₁ is a block diagonal matrix, the blockdiagonal matrix includes at least one block matrix, and each blockmatrix is a function of the user equipment-specific matrix or matrixset.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a fourth implementation manner of thefifth aspect, each block matrix X is a Kronecker product of two matricesC and D , X=C⊗D, and at least one matrix in the two matrices C and D isa function of the user equipment-specific matrix or matrix set.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a fifth implementation manner of thefifth aspect, that at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set includesthat:

a k^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a _(m)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shifts.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a sixth implementation manner of thefifth aspect, a matrix in the user equipment-specific matrix or matrixset is a matrix formed by columns being discrete Fourier transformationDFT vectors, or a matrix formed by column vectors of a Hadamard matrixor a Householder matrix.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a seventh implementation manner of thefifth aspect, the DFT vector a_(l) satisfies:

${a_{l} = \begin{bmatrix}e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}} & e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}} & \ldots & e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}\end{bmatrix}^{T}},$

where []^(T) is a matrix transpose, M and N are positive integers, andN_(C)≥N or N_(D)≥N.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in an eighth implementation manner of thefifth aspect, the first reference signal set includes at least onereference signal subset, and the reference signal subset is associatedwith a set of the matrix C or the matrix D.

With reference to the fifth aspect and the foregoing implementationmanners of the fifth aspect, in a ninth implementation manner of thefifth aspect, the reference signal subset has a sending period longerthan that of another reference signal.

According to a sixth aspect, a base station is provided, including: atransmitter, configured to send a first reference signal set to userequipment, where the first reference signal set is associated with auser equipment-specific matrix or matrix set; and a receiver, configuredto receive a precoding matrix indicator PMI sent by the user equipment,where the PMI is used for indicating a precoding matrix that is selectedbased on the first reference signal set by the user equipment, and theprecoding matrix is a function of a subset of the userequipment-specific matrix or matrix set.

With reference to the sixth aspect and the foregoing implementationmanner of the sixth aspect, in a first implementation manner of thesixth aspect, the transmitter is further configured to notify the userequipment of the user equipment-specific matrix or matrix set.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a second implementation manner of thesixth aspect, the first reference signal set includes one or morereference signal subsets, and the reference signal subset corresponds toa co-polarized antenna port subset, or corresponds to an antenna portsubset that is arranged in a same direction in an antenna port array, orcorresponds to a quasi-co-location antenna port subset.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a third implementation manner of thesixth aspect, the precoding matrix w is a product of two matrices W₁ andW₂, W=W₁W₂, where the matrix W₁ is a block diagonal matrix, the blockdiagonal matrix includes at least one block matrix, and each blockmatrix is a function of the user equipment-specific matrix or matrixset.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a fourth implementation manner of thesixth aspect, each block matrix X is a Kronecker product of two matricesc and D, X=C⊗D, and at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a fifth implementation manner of thesixth aspect, that at least one matrix in the two matrices C and D is afunction of the user equipment-specific matrix or matrix set includesthat:

a k^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a _(m)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shifts.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a sixth implementation manner of thesixth aspect, a matrix in the user equipment-specific matrix or matrixset is a matrix formed by columns being discrete Fourier transformationDFT vectors, or a matrix formed by column vectors of a Hadamard matrixor a Householder matrix.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a seventh implementation manner of thesixth aspect, that columns of the matrix in the user equipment-specificmatrix or matrix set are discrete Fourier transformation DFT vectorsincludes that: the DFT vector a_(l) satisfies:

${a_{l} = \begin{bmatrix}e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}} & e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}} & \ldots & e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}\end{bmatrix}^{T}},$

where []^(T) is a matrix transpose, M and N are positive integers, andN_(C)≥N or N_(D)≥N.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in an eighth implementation manner of thesixth aspect, the first reference signal set includes at least onereference signal subset, and the reference signal subset is associatedwith a set of the matrix C or the matrix D.

With reference to the sixth aspect and the foregoing implementationmanners of the sixth aspect, in a ninth implementation manner of thesixth aspect, the first reference signal set includes at least onereference signal subset, and the reference signal subset has a sendingperiod longer than that of another reference signal.

In the embodiments of the present invention, a first reference signalset is associated with a user equipment-specific matrix or matrix set, aprecoding matrix is a function of the user equipment-specific matrix ormatrix set, so that user equipment can select, based on the userequipment-specific matrix or matrix set, the precoding matrix and feedback a PMI, and a set of the precoding matrix forms a userequipment-specific codebook but not a cell specific codebook or systemspecific codebook. The cell specific codebook or system specificcodebook is a precoding matrix set designed for all users in a cell or asystem, while the user equipment-specific codebook is a subset of thecell specific codebook or system specific codebook. Therefore, in theembodiments of the present invention, CSI feedback precision can beimproved without excessively increasing feedback overhead, therebyimproving system performance.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly introduces theaccompanying drawings required for describing the embodiments.Apparently, the accompanying drawings in the following description showmerely some embodiments of the present invention, and a person ofordinary skill in the art may still derive other drawings from theseaccompanying drawings without creative efforts.

FIG. 1 is a flowchart of a method for determining a precoding matrixindicator according to an embodiment of the present invention;

FIG. 2 is a flowchart of a method for determining a precoding matrixindicator according to another embodiment of the present invention;

FIG. 3 is a schematic flowchart of a multi-antenna transmission methodaccording to an embodiment of the present invention;

FIG. 4 is a block diagram of user equipment according to an embodimentof the present invention;

FIG. 5 is a block diagram of a base station according to an embodimentof the present invention;

FIG. 6 is a block diagram of user equipment according to anotherembodiment of the present invention; and

FIG. 7 is a block diagram of a base station according to anotherembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The following clearly describes the technical solutions in theembodiments of the present invention with reference to the accompanyingdrawings in the embodiments of the present invention. Apparently, thedescribed embodiments are some but not all of the embodiments of thepresent invention. All other embodiments obtained by a person ofordinary skill in the art based on the embodiments of the presentinvention without creative efforts shall fall within the protectionscope of the present invention.

The technical solutions of the present invention may be applied tovarious communications systems, such as: a Global System for MobileCommunications (GSM), a Code Division Multiple Access (CDMA) system, aWideband Code Division Multiple Access (WCDMA), a general packet radioservice (GPRS), and a Long Term Evolution (LTE) system.

User equipment (UE), also referred to as a mobile terminal, a mobileuser equipment, and the like, may communicate with one or more corenetworks through a radio access network (RAN). The user equipment may bea mobile terminal, such as a mobile phone (also referred to as a“cellular” phone) and a computer with a mobile terminal. For example,the user equipment may be a portable, pocket-sized, handheld, computerbuilt-in, or in-vehicle mobile apparatus, or may be a relay, and theuser equipment exchanges language and/or data with the radio accessnetwork.

A base station may be a base station (BTS) in the GSM or CDMA, may alsobe a base station (NodeB) in the WCDMA, and may further be an evolvedNodeB (eNB or e-NodeB, evolved Node B) or relay in the LTE, which is notlimited in the present invention.

FIG. 1 is a flowchart of a method for determining a precoding matrixindicator according to an embodiment of the present invention. Themethod in FIG. 1 is executed by user equipment (UE).

101: Receive a first reference signal set sent by a base station, wherethe first reference signal set is associated with a userequipment-specific (UE-specific) matrix or matrix set.

102: Select a precoding matrix based on the first reference signal set,where the precoding matrix is a function of a user equipment-specificmatrix or matrix set.

103: Send a precoding matrix indicator PMI to the base station, wherethe PMI corresponds to the selected precoding matrix.

In this embodiment of the present invention, a first reference signalset is associated with a user equipment-specific matrix or matrix set, aprecoding matrix is a function of the user equipment-specific matrix ormatrix set, so that user equipment can select, based on the userequipment-specific matrix or matrix set, the precoding matrix and feedback a PMI, and a set of the precoding matrix forms a userequipment-specific codebook but not a cell specific codebook or systemspecific codebook. The cell specific codebook or system specificcodebook is a precoding matrix set designed for all users in a cell or asystem, while the user equipment-specific codebook is a subset of thecell specific codebook or system specific codebook. Therefore, in thisembodiment of the present invention, CSI feedback precision can beimproved without excessively increasing feedback overhead, therebyimproving system performance.

It should be understood that a matrix may include a multi-rowmulti-column matrix, or may also include a multi-row single-columnvector, a single-row multi-column vector, or a scalar (single-rowsingle-column matrix).

Optionally, as an embodiment, the user equipment-specific matrix ormatrix set is notified by the base station to the user equipment.

Optionally, as another embodiment, before step 101, the user equipmentmay further receive a second reference signal set sent by the basestation, where the second reference signal set is associated with amatrix or matrix set. Based on the second reference signal set, the userequipment determines and sends a second index to the base station. Thesecond index is used for indicating an antenna port or antenna portsubset selected by the user equipment, or a subset of a matrix or matrixset that is associated with the antenna port or antenna port subsetselected by the user equipment.

Optionally, the first reference signal set may be a subset of the secondreference signal set.

Optionally, as another embodiment, when receiving the second referencesignal set sent by the base station, the user equipment may receivereference signals of the second reference signal set that are sent atdifferent times by the base station. Here, different times may beassociated with a same matrix or different matrices separately, or maybe associated with a same subset or different subsets of a matrix setseparately.

Optionally, the matrix or matrix set associated with the secondreference signal set is cell specific or system specific.

Optionally, as another embodiment, the first reference signal setincludes one or more reference signal subsets, and the reference signalsubset corresponds to a co-polarized antenna port subset, or correspondsto an antenna port subset that is arranged in a same direction in anantenna port array, or corresponds to a quasi-co-location (QCL) antennaport subset.

Optionally, as another embodiment, when receiving the first referencesignal set sent by the base station, the user equipment may receivereference signals of the first reference signal set that are sent atdifferent times by the base station. Here, different times may beassociated with a same matrix or different matrices separately, or maybe associated with a same subset or different subsets of a matrix setseparately.

Optionally, as another embodiment, the precoding matrix w is a productof two matrices W₁ and W₂.

W=W₁W₂  (1)

The matrix W₁ is a block diagonal matrix. The block diagonal matrixincludes at least one block matrix, and each block matrix is a functionof the user equipment-specific matrix or matrix set.

Optionally, the matrix W₂ is used to select or perform weightedcombination on column vectors in the matrix W₁, so as to form the matrixw.

Optionally, as another embodiment, each block matrix X is a Kroneckerproduct of two matrices C and D, X=C⊗D. At least one matrix in the twomatrices C and D is a function of the user equipment-specific matrix ormatrix set.

Optionally, as another embodiment, columns of at least one matrix in thetwo matrices C and D are rotations of column vectors in a matrix in asubset of the user equipment-specific matrix or matrix set, that is, ak^(th) column vector c_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),  (3)

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m),  (5)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }a_(m),  (4)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)   (5)

where N_(V), N_(H), N_(C), and N_(D) are positive integers, a_(m) is anm^(th) column vector of a matrix A, the matrix A is a matrix in the userequipment-specific matrix or matrix set, and θ and ϕ are phase shiftswhose values may be 0,π, ±π/2, ±π/4, ±π/8, and so on.

It should be noted that a value of N_(C) or N_(D) may be infinite, andtherefore 2π/N_(C)=0 or 2π/N_(D)=0, and in this case, c_(k)=a_(m),c_(k)=diag{1,1, . . . ,1,e^(jθ),e^(jθ), . . . ,e^(jθ)}a_(m), d_(l)=a_(m)or d_(l)=diag{1,1, . . . ,1,e^(jϕ),e^(jϕ), . . . ,e^(jϕ)}a_(m).

It should be noted that, that column vectors of the matrix C or matrix Dthat correspond to the block matrix X at a different location on adiagonal in W₁ satisfy the expressions (2) to (5) does not mean that theblock matrix X at a different location on a diagonal in W₁ has a samematrix C or matrix D. In contrast, the block matrix X at a differentlocation may have a same or different matrix C or matrix D.

Optionally, as another embodiment, a matrix in the userequipment-specific matrix or matrix set is a matrix formed by columnsbeing discrete Fourier transformation (DFT) vectors, or a matrix formedby column vectors of a Hadamard matrix or a Householder matrix.

Optionally, as another embodiment, the DFT vector a_(l) satisfies:

$\begin{matrix}{a_{l} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot l}}{N}}\mspace{20mu} e^{j\frac{2{\pi \cdot 1 \cdot l}}{N}}\mspace{20mu} \ldots \mspace{20mu} e^{j\frac{2{\pi \cdot {({M - 1})} \cdot l}}{N}}} \right\rbrack^{T}} & (6)\end{matrix}$

-   -   where []^(T) is a matrix transpose, M and N are positive        integers, and N_(C)≥N or N_(D)≥N.

Optionally, as another embodiment, the first reference signal setincludes at least one reference signal subset, and the reference signalsubset is associated with a set of the matrix C or the matrix D.

Optionally, as another embodiment, the reference signal subset has asending period longer than that of another reference signal.

As an embodiment of the present invention, the precoding matrix w may bethe following matrix:

$\mspace{20mu} {{\left( {2M} \right)^{- \frac{1}{2}}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}\mspace{20mu} e^{j\; \phi}\mspace{14mu} e^{j{({\phi + \theta})}}\mspace{14mu} \ldots \mspace{14mu} e^{j{({\phi + {{({M - 1})}\theta}})}}} \right\rbrack}^{T}\mspace{14mu} {{{or}\text{}\left( {4M} \right)}^{- \frac{1}{2}}\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}\mspace{20mu} e^{j\; \varphi}\mspace{14mu} e^{j{({\varphi + \theta})}}\mspace{14mu} \ldots \mspace{14mu} e^{j{({\varphi + {{({M - 1})}\theta}})}}} \right\rbrack^{T} \\{e^{j\; \phi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}\mspace{20mu} e^{j\; \varphi}\mspace{14mu} e^{j{({\varphi + \theta})}}\mspace{14mu} \ldots \mspace{14mu} e^{j{({\varphi + {{({M - 1})}\theta}})}}} \right\rbrack}^{T}\end{bmatrix}}\mspace{14mu} {{{or}\mspace{20mu}\left( {2{NM}} \right)}^{- \frac{1}{2}}\begin{bmatrix}\begin{bmatrix}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} \\\ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix} \\{e^{j\; \phi}\begin{bmatrix}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} \\\ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix}}\end{bmatrix}}\mspace{14mu} {where}}$${\phi = 0},{\pi/2},\pi,{3{\pi/2}\mspace{11mu} \ldots}\;,{\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \;,15,{i_{2} = 0},\ldots \;,15,$

and a symbol “└x┘” represents a maximum integer that is not greater thanx.

${\varphi = \frac{k\pi}{32}},$

k=0, . . . ,15, . . . ,32, and so on, or k=0, ±1, . . . , ±15, ±16, andso on.

M is a positive integer; for example, a value of M may be 1, 2, 4, 6, 8,16, 32, 64, and so on. N is a positive integer; for example, a value ofN may be 1, 2, 4, 6, 8, 16, 32, 64, and so on.

As another embodiment of the present invention, the precoding matrix wmay be the following matrix:

${{\left( {4{NM}} \right)^{- \frac{1}{2}}\begin{bmatrix}\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} & \left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} \\\ldots & \ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix} \\\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} & {- \left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T}} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {- {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\\ldots & \ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {- {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}}\end{bmatrix}\end{bmatrix}}\mspace{14mu} {{{or}\left( {4{NM}} \right)}^{- \frac{1}{2}}\begin{bmatrix}\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} & \left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\\ldots & \ldots \\{\; {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix} \\\begin{bmatrix}{j\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {- {j\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\{j\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {{- j}\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\\ldots & \ldots \\{j\; {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {{- j}\; {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}}\end{bmatrix}\end{bmatrix}}}\mspace{11mu}$  where$\mspace{20mu} {{\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \;,15,{i_{2} = 0},\ldots \;,15,}$

and a symbol “└x┘” represents a maximum integer that is not greater thanx.

${\varphi = \frac{k\pi}{32}},$

k=0, . . . ,15, . . . ,32, and so on, or k=0,±1, . . . ,±15,±16, and soon.

M is a positive integer; for example, a value of M may be 1, 2, 4, 6, 8,16, 32, 64, and so on. N is a positive integer; for example, a value ofN may be 1, 2, 4, 6, 8, 16, 32, 64, and so on.

It can be known from studying the precoding matrix w, the precodingmatrix w may match an actually deployed antenna configuration; becausegranularity of a value of θ is π/16, more precise space quantization canbe implemented, and feedback precision of CSI can be improved; besides,two columns of the precoding matrix w are orthogonal to each other, andinterference between layers can be reduced.

FIG. 2 is a flowchart of a method for determining a precoding matrixindicator according to another embodiment of the present invention. Themethod in FIG. 2 is executed by a base station (for example, eNB).

201: Send a first reference signal set to user equipment, where thefirst reference signal set is associated with a user equipment-specific(UE-specific) matrix or matrix set.

202: Receive a precoding matrix indicator PMI sent by the userequipment, where the PMI is used for indicating a precoding matrix thatis selected based on the first reference signal by the user equipment,and the precoding matrix is a function of the user equipment-specificmatrix or matrix set.

In this embodiment of the present invention, a first reference signalset is associated with a subset of a user equipment-specific matrix ormatrix set, a precoding matrix is a function of the userequipment-specific matrix or matrix set, so that user equipment canselect, based on the subset of the matrix or matrix set, the precodingmatrix and feed back a PMI, and a set of the precoding matrix forms auser equipment-specific codebook but not a cell specific codebook orsystem specific codebook. The cell specific codebook or system specificcodebook is a precoding matrix set designed for all users in a cell or asystem, while the user equipment-specific codebook is a subset of thecell specific codebook or system specific codebook. Therefore, in thisembodiment of the present invention, CSI feedback precision can beimproved without excessively increasing feedback overhead, therebyimproving system performance.

Optionally, the precoding matrix may also be obtained according to thereceived PMI.

Optionally, as an embodiment, the user equipment-specific matrix ormatrix set is notified by the base station to the user equipment.

Optionally, as another embodiment, before step 201, the base station mayfurther send a second reference signal set to the user equipment, wherethe second reference signal set is associated with a matrix or matrixset. Then, the base station receives a second index that is determinedbased on the second reference signal set by the user equipment. Thesecond index is used for indicating an antenna port or antenna portsubset selected by the user equipment, or a matrix or matrix set that isassociated with the antenna port or antenna port subset selected by theuser equipment.

Optionally, the first reference signal set is a subset of the secondreference signal set.

Optionally, as another embodiment, when sending the second referencesignal set to the user equipment, the base station may send referencesignals of the second reference signal set to the user equipment atdifferent times.

Optionally, the matrix or matrix set associated with the secondreference signal set is cell specific or system specific.

Optionally, as an embodiment, before step 201, the base station mayfurther measure an uplink physical channel or an uplink physical signal,to obtain channel estimation of the user equipment according to channelreciprocity. Based on a predefined criterion, the first reference signaland the user equipment-specific matrix or matrix set are selected for auser. The uplink physical channel may be a physical uplink controlchannel (PUCCH) or a physical uplink shared channel (PUSCH); thephysical signal may be a sounding reference signal (SRS) or anotheruplink demodulation reference signal (DMRS).

Optionally, as another embodiment, the first reference signal set mayinclude one or more reference signal subsets. The reference signalsubset corresponds to a co-polarized antenna port subset, or correspondsto an antenna port subset that is arranged in a same direction in anantenna port array, or corresponds to a quasi-co-location antenna portsubset.

Optionally, as another embodiment, in step 201, the base station maysend subsets of the first reference signal set to the user equipment atdifferent times. Here, different times may be associated with a samematrix or different matrices separately, or may be associated with asame subset or different subsets of a matrix set separately.

Optionally, as another embodiment, the precoding matrix w is a productof two matrices W₁ and W₂, W=W₁W₂, where the matrix W₁ is a blockdiagonal matrix, the block diagonal matrix includes at least one blockmatrix, and each block matrix is a function of the userequipment-specific matrix or matrix set.

Optionally, the matrix W₂ is used to select or perform weightedcombination on column vectors in the matrix W₁, so as to form the matrixw.

Optionally, as another embodiment, each block matrix X is a Kroneckerproduct of two matrices C and D, X=C⊗D. At least one matrix in the twomatrices C and D is a function of the user equipment-specific matrix ormatrix set.

Optionally, as another embodiment, columns of at least one matrix in thetwo matrices C and D are rotations of column vectors in a matrix in theuser equipment-specific matrix or matrix set, that is, a k^(th) columnvector c_(k) of the matrix C is shown in the expression (2) or (3); oran l^(th) column vector d_(l) of the matrix D is shown in the expression(4) or (5), where N_(V), N_(H), N_(C), and N_(D) are positive integers,a_(m) is an m^(th) column vector of a matrix A, and the matrix A is amatrix in the user equipment-specific matrix or matrix set.

It should be noted that, that column vectors of the matrix C or matrix Dthat corresponds to the block matrix X at a different location on adiagonal in W₁ satisfy the expressions (2) to (5) does not mean that theblock matrix X at a different location on a diagonal in W₁ has a samematrix C or matrix D. In contrast, the block matrix X at a differentlocation may have a same or different matrix C or matrix D.

Optionally, as another embodiment, a matrix in the userequipment-specific matrix or matrix set is a matrix formed by columnsbeing DFT vectors, or a matrix formed by column vectors of a Hadamardmatrix or a Householder matrix.

Optionally, as another embodiment, the DFT vector a_(l) is shown in theexpression (6), where N_(C)≥N or N_(D)≥N.

Optionally, as another embodiment, the first reference signal setincludes at least one reference signal subset, and the reference signalsubset is associated with a set of the matrix C or the matrix D.

Optionally, as another embodiment, the reference signal subset has asending period longer than that of another reference signal.

As an embodiment of the present invention, the precoding matrix W may bethe following matrix:

$\mspace{20mu} {{\left( {2M} \right)^{- \frac{1}{2}}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}\mspace{20mu} e^{j\; \phi}\mspace{14mu} e^{j{({\phi + \theta})}}\mspace{14mu} \ldots \mspace{14mu} e^{j{({\phi + {{({M - 1})}\theta}})}}} \right\rbrack}^{T}\mspace{14mu} {{{or}\text{}\left( {4M} \right)}^{- \frac{1}{2}}\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}\mspace{20mu} e^{j\; \varphi}\mspace{14mu} e^{j{({\varphi + \theta})}}\mspace{14mu} \ldots \mspace{14mu} e^{j{({\varphi + {{({M - 1})}\theta}})}}} \right\rbrack^{T} \\{e^{j\; \phi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}\mspace{20mu} e^{j\; \varphi}\mspace{14mu} e^{j{({\varphi + \theta})}}\mspace{14mu} \ldots \mspace{14mu} e^{j{({\varphi + {{({M - 1})}\theta}})}}} \right\rbrack}^{T}\end{bmatrix}}\mspace{14mu} {{{or}\mspace{20mu}\left( {2{NM}} \right)}^{- \frac{1}{2}}\begin{bmatrix}\begin{bmatrix}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} \\\ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix} \\{e^{j\; \phi}\begin{bmatrix}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{20mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} \\\ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{14mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{20mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix}}\end{bmatrix}}\mspace{14mu} {where}}$${\phi = 0},{\pi/2},\pi,{3{\pi/2}\mspace{11mu} \ldots}\;,{\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \;,15,{i_{2} = 0},\ldots \;,15,$

and a symbol └x┘ represents a maximum integer that is not greater thanx.

${\varphi = \frac{k\pi}{32}},$

k=0, . . . ,15, . . . ,32 , and so on, or k=0,±1, . . . ,±15,±16 , andso on.

M is a positive integer; for example, a value of M may be 1, 2, 4, 6, 8,16, 32, 64, and so on. N is a positive integer; for example, a value ofN may be 1, 2, 4, 6, 8, 16, 32, 64, and so on.

As another embodiment of the present invention, the precoding matrix wmay be the following matrix:

${{\left( {4{NM}} \right)^{- \frac{1}{2}}\begin{bmatrix}\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} & \left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} \\\ldots & \ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix} \\\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} & {- \left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T}} \\{e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {- {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\\ldots & \ldots \\{e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {- {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}}\end{bmatrix}\end{bmatrix}}\mspace{14mu} {{{or}\left( {4{NM}} \right)}^{- \frac{1}{2}}\begin{bmatrix}\begin{bmatrix}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} & \left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack^{T} \\{\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\\ldots & \ldots \\{\; {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}\end{bmatrix} \\\begin{bmatrix}{j\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T} & {- {j\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\{j\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {{- j}\; {e^{j\; \varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} \\\ldots & \ldots \\{j\; {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}} & {{- j}\; {e^{{j{({N - 1})}}\varphi}\left\lbrack {1\mspace{20mu} e^{j\; \theta}\mspace{14mu} \ldots \mspace{14mu} e^{{j{({M - 1})}}\theta}} \right\rbrack}^{T}}\end{bmatrix}\end{bmatrix}}}\mspace{14mu}$ where$\mspace{20mu} {{\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \;,15,{i_{2} = 0},\ldots \;,15,}$

and a symbol “└x┘” represents a maximum integer that is not greater thanx.

${\varphi = \frac{k\pi}{32}},$

k=0, . . . ,15, . . . ,32, and so on, or k=0,±1, . . . ,±15,±16, and soon.

M is a positive integer; for example, a value of M may be 1, 2, 4, 6, 8,16, 32, 64, and so on. N is a positive integer; for example, a value ofN may be 1, 2, 4, 6, 8, 16, 32, 64, and so on.

It can be known from studying the precoding matrix w, the precodingmatrix w may match an actually deployed antenna configuration; becausegranularity of a value of θ is π/16, more precise space quantization canbe implemented, and feedback precision of CSI can be improved; besides,two columns of the precoding matrix w are orthogonal to each other, andinterference between layers can be reduced.

The embodiments of the present invention are described below in moredetail with reference to specific examples. In embodiments describedbelow, an eNB is used as an example of a base station, and UE is used asan example of user equipment, but the embodiments of the presentinvention are not limited thereto, and may also be applied to othercommunications systems.

FIG. 3 is a schematic flowchart of a multi-antenna transmission methodaccording to an embodiment of the present invention.

301: UE receives a first reference signal set, where the first referencesignal set is associated with a user equipment-specific (UE-specific)matrix or matrix set.

Specifically, the first reference signal set received by the UE isnotified by an eNB by using higher layer signaling, or is dynamicallynotified by an eNB by using a downlink control channel. The referencesignal may be a cell specific reference signal (CRS, Cell specific RS),or a demodulation reference signal (DMRS, DeModulation RS), or a channelstate information reference signal (CSI-RS, channel state informationRS). The reference signal may correspond to a physical antenna, or mayalso correspond to a virtual antenna, where the virtual antenna is aweighted combination of multiple physical antennas.

The first reference signal set may include one or more reference signalsubsets.

Specifically, for example, the first reference signal set received bythe UE is P, which includes in total eight reference signals, namely,p1, p2, p3, . . . , p7, and p8. The first reference signal set mayinclude one reference signal subset. In this case, the reference signalsubset is the same as the first reference signal set, that is, the eightreference signals p1, p2, . . . , and p8 in P.

Alternatively, the first reference signal set may include multiplereference signal subsets. For example, the first reference signal set isP, and includes two reference signal subsets P1 and P2, where P1={p1,p2, p3, p4}, and P2 ={p5, p6, p7, p8}.

Further, the reference signal subset included in the first referencesignal set may correspond to a co-polarized antenna port subset. Forexample, the subset P1={p1, p2, p3, p4} of the first reference signalset corresponds to a co-polarized antenna port subset; and the subsetP2={p5, p 6, p7, p8} of the first reference signal set corresponds toanother co-polarized antenna port subset.

Optionally, as another embodiment, the reference signal subset includedin the first reference signal set may correspond to a port subset thatis arranged in a same direction in an antenna port array. For example,the subset P1={p1, p2, p3, p4} of the first reference signal setcorresponds to an antenna port subset of a column in a verticaldirection in the antenna port array. The subset P2={p5, p6, p7, p8} ofthe first reference signal set corresponds to an antenna port subset ofa row in a horizontal direction in the antenna port array.Alternatively, P1={p1, p2, p3, p4} and P2={p5, p 6, p7, p8} correspondto antenna port subsets of two different rows in the antenna port arrayseparately. Alternatively, P1={p1, p2, p3, p4} and P2={p5, p6, p7, p8}correspond to antenna port subsets of two different columns in theantenna port array separately.

Optionally, as another embodiment, the reference signal subset includedin the first reference signal set may correspond to a quasi-co-locationantenna port subset. For example, the subset P1={p1, p2, p3, p4} of thefirst reference signal set corresponds to a quasi-co-location antennaport subset. The subset P2={p5, p6, p7, p8} of the first referencesignal set corresponds to an antenna port subset that is located atanother quasi-co-location. It should be noted that the quasi-co-location(QCL) antenna port refers to that a distance between antennascorresponding to the antenna port is within a range that uses awavelength as a dimension.

It should be noted that each of the foregoing antenna ports correspondto a physical antenna or virtual antenna, where the virtual antenna is aweighted combination of multiple physical antennas or antenna arrayelements.

Further, reference signals in the multiple reference signal subsetsincluded in the first reference signal set may occupy differentsymbol/frequency/sequence resources and be transmitted at a samesubframe, or may occupy a same symbol/frequency/sequence resource and betransmitted at different subframes.

The foregoing division of the reference signal subset may further reducecomplexity of implementation.

Specifically, the first reference signal set is associated with a subsetof a user equipment-specific (UE-specific) matrix or matrix set; or eachreference signal in the first reference signal set may be associatedwith a subset of a user equipment-specific (UE-specific) matrix ormatrix set. For example, the reference signal set notified by the eNB isS, which includes in total eight reference signals, namely s1, s2, s3, .. . , s7, and s8. The foregoing reference signals are associated withmatrices w1, w2, , and w8 separately, or are associated with {w1,w2},{w2,w3}, . . . , {w7,w8}, and {w8,w1 } separately.

The first reference signal set is associated with a subset of a matrixor matrix set, or a reference signal subset of the first referencesignal set may be associated with a subset of a user equipment-specificmatrix or matrix set. For example, the reference signal set notified bythe eNB is S, which includes in total eight reference signals, namelys1, s2, s3, . . . , s7, and s8. A reference signal subset {s1, s2, s3,s4} is associated with a matrix p1 or a matrix subset {p1, , pm}, and areference signal subset {s5, s6, s7, s8} is associated with a matrix w1or a matrix subset {w1, . . . , wn}, where m and n are positiveintegers. Alternatively, reference signal subsets {s1, s2}, {s3, s4}, .. . , and {s7, s8} are associated with matrices w1, w2, w3, and w4respectively. Alternatively, reference signal subsets {s1, s2}, {s3,s4}, . . . , and {s7, s8} are associated with matrices {w1, w2}, {w3,w4}, . . . , and {w7, w8} respectively. The matrix herein includes avector.

Further, an association or a correspondence between the first referencesignal set and a user equipment-specific matrix or matrix set may beindicated by using signaling. For example, it is indicated by usinghigher layer signaling, for example, radio resource control (RRC)signaling, that the reference signal subset {s1, s2, s3, s4} isassociated with a matrix p1 or a matrix subset {p1, . . . , pm}, and thereference signal subset {s5, s6, s7, s8} is associated with a matrix w1or a matrix subset {w1, . . . , wn}. Alternatively, the association orcorrespondence between the first reference signal set and a userequipment-specific matrix or matrix set is dynamically indicated byusing downlink control information (DCI). Alternatively, multiplecandidate association relationships are indicated by using higher layersignaling, for example RRC signaling, and one of the candidateassociation relationships is further dynamically indicated by using DCI.Specifically, each matrix subset in the signaling may be represented bya bitmap. The RRC signaling may be UE-specific signaling, for example,dedicated physical signaling. Besides, the first reference signal setand indication information of the UE-specific matrix or matrix set maybe sent in same RRC dedicated signaling.

Optionally, as another embodiment, an association relationship ormapping between the first reference signal set and a userequipment-specific matrix or matrix set may also be predefined. Forexample, it is predefined and known by both the user equipment and thebase station that the reference signal subset {s1, s2, s3, s4} isassociated with a matrix pl or a matrix subset {p1, . . . , pm}, and thereference signal subset {s5, s6, s7, s8} is associated with a matrix w1or a matrix subset {w1, . . . , wn}.

Specifically, the first reference signal set is associated with a subsetof a matrix or matrix set, or the first reference signal set may beassociated with a matrix or matrix set, where a subset of the matrix ormatrix set is notified by using signaling or is predefined. For example,a matrix or matrix subset is notified by using higher layer signaling,for example, RRC signaling, or is dynamically notified by using DCI; ora matrix set is notified by using higher layer signaling, for example,RRC signaling, and one matrix subset in the matrix set is furtherdynamically notified by using DCI.

Specifically, a matrix A in a subset of the matrix or matrix set that isassociated with the first reference signal set may be a matrix formed bycolumns being DFT vectors, that is,

A=[a ₀ a ₁ . . . a _(N) _(a) ⁻¹],  (7)

where,

a _(k) ϵ{f ₀ ,f ₁ , . . . ,f _(N) _(f) ⁻¹ }, k=0, . . . , N _(a)−1  (8)

where N_(a)≥1 is a quantity of columns of the matrix A, and N_(f)≥1 is aquantity of columns of the DFT vectors; f_(n),n=0, . . . , N_(f)−1 isthe DFT vectors, that is, f_(n) is represented as:

$\begin{matrix}{f_{n} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot n}}{N}}\mspace{20mu} e^{j\frac{2{\pi \cdot 1 \cdot n}}{N}}\mspace{14mu} \ldots \mspace{20mu} e^{j\frac{2{\pi \cdot {({M - 1})} \cdot n}}{N}}} \right\rbrack^{T}} & (9)\end{matrix}$

where both M and N are integers; for example, for M=N=4, there is:

$\begin{matrix}{\left\lbrack {f_{0}\mspace{20mu} f_{1}\mspace{20mu} f_{2}\mspace{20mu} f_{3}} \right\rbrack = {\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & j & {- 1} & {- j} \\1 & {- 1} & 1 & {- 1} \\1 & {- j} & {- 1} & j\end{bmatrix}}} & (10)\end{matrix}$

Specifically, a matrix A in the user equipment-specific (UE specific)matrix or matrix set may also be a matrix formed by column vectors of aHadamard matrix, that is

A=[a ₀ a ₁ . . . a _(N) _(a) ⁻¹],  (11)

where,

a _(k) ϵ{f ₀ ,f ₁ , . . . ,f _(N) _(f) ⁻¹ }, k=0, . . . , N _(a)−1  (12)

where N_(a)≥1 is a quantity of columns of the matrix A, N_(h)≥1 is aquantity of columns of the Hadamard matrix, and h_(m), m=0, . . . ,N_(h)−1 is column vectors of the Hadamard matrix, for example,

$\begin{matrix}{\left\lbrack {h_{0}\mspace{20mu} h_{1}\mspace{20mu} h_{2}\mspace{20mu} h_{3}} \right\rbrack = {\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}}} & (13)\end{matrix}$

Further, the user equipment-specific (UE specific) matrix set mayinclude at least two matrices, where one matrix is the matrix Adescribed above, and the other matrix is a matrix B formed by columnsbeing DFT vectors, or by column vectors of a Hadamard matrix, that is,

B=[b ₀ b ₁ . . . b _(N) _(b−1) ],  (14)

where,

b _(k) ϵ{f′ ₀ ,f′ ₁ , . . . ,f′ _(N′) _(f) ⁻¹ }, k=0, . . . ,N_(b)−1  (15)

or

b _(k) ϵ{h′ ₀ ,h′ ₁ , . . . ,h′ _(N′) _(f) ⁻¹ }, k=0, . . . ,N_(b)−1  (16)

where N_(b)≥1 is a quantity of columns of the matrix B, N′_(h)≥1 andN′_(f)≥1 are a quantity of columns of the Hadamard matrix and a quantityof columns of the DFT vectors respectively; h′_(m) is a column vector ofthe Hadamard matrix; f′_(n) is the DFT vectors, that is, f′_(n) isrepresented as:

$\begin{matrix}{f_{n}^{\prime} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot n}}{N^{\prime}}}\mspace{20mu} e^{j\frac{2{\pi \cdot 1 \cdot n}}{N^{\prime}}}\mspace{14mu} \ldots \mspace{20mu} e^{j\frac{2{\pi \cdot {({M^{\prime} - 1})} \cdot n}}{N^{\prime}}}} \right\rbrack^{T}} & (17)\end{matrix}$

where M′,N′ are both integers; in this case, the first reference signalset may be divided into two subsets, which are separately associatedwith the matrix A and the matrix B or a subset formed by the matrix Aand a subset formed by the matrix B.

Alternatively, one matrix in the user equipment-specific (UE specific)matrix or the matrix set may also be a matrix Y in the following form:

Y=A⊗B  (18)

where A and B may have the foregoing structures shown in the expressions(8) to (13) and the expressions (14) to (17) respectively.

Besides, the matrix in the user equipment-specific (UE specific) matrixor the matrix set may also use a matrix in another form, for example, aHouseholder matrix, or a precoding matrix in an LTE R8 4-antenna or LTER10 8-antenna codebook.

One matrix in the user equipment-specific (UE specific) matrix or thematrix set may have the following structure:

W=W₁W₂  (19)

where a matrix W₁ is a block diagonal matrix, for example,

W ₁=diag {X ₁ ,X ₂}  (20)

where each block matrix in the matrix W₁ is a function of the matrices Aand B or a function of a matrix Y, for example,

X _(i)=diag{ρ₀,ρ₁ , . . . ,} A⊗B, i=1,2  (21)

or

X _(i)=diag {ρ₀,ρ₁ , . . . ,}Y, i=1,2  (22)

where ρ₀,ρ₁. . . , are scalars; for example, ρ₀=ρ₁=, . . . ,=1.

Optionally, as another embodiment, each block matrix in the matrix W₁may be represented as a Kronecker product of two matrices, for example,

X _(i) =C _(i) ⊗D _(i) , i=1,2,  (23)

where ⊗ represents a matrix Kronecker product, and a matrix C_(i) orD_(i) satisfies the following relationship:

A k^(th) column c_(l) of the matrix C, satisfies:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m)  (24)

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)  (25)

or an l^(th) column d_(l) of D satisfies:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }b_(n)  (25)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }a _(m)  (27)

where N_(V), N_(H), N_(C), and N_(D) are all positive integers, vectorsa_(l) and b_(l) are columns of the matrix A and the matrix Brespectively, and θ and ϕ are phase shifts whose values may be0,π,±π/2,±π/4,±π/8, and so on.

It should be noted that a value of N_(C) or N_(D) may be infinite, andtherefore 2π/N_(C)=0 or 2π/N_(D)=0, and in this case, c_(k)=a_(m),c_(k)=diag{1,1, . . . ,1,e^(jθ),e^(jθ), . . . ,e^(jθ)}a_(m),d_(i)=a_(m), or d_(l)=diag{1,1, . . . ,1,e^(jϕ),e^(jϕ), . . .,e^(jϕ)}a_(m).

Further, vectors c_(k) and d_(k) in the expressions (24) to (27) mayhave granularity finer than that of a_(l) and b_(l) respectively, thatis,

N_(C)≥N or N_(D)≥N′  (28)

Further, a set formed by the foregoing vector or matrix A or B or Y or Wis C_(A) or C_(B) or C_(Y) or C_(W), and may be further divided intomultiple subsets (the subset may include only one element), and eachsubset may be associated with or have a mapping relationship with a userequipment identifier. For example, a subset C_(A) ⁽¹⁾ in C_(A) isassociated with or is mapped to a user equipment identifier ID₁, andanother subset C_(A) ⁽²⁾ in C_(A) is associated with or is mapped to auser equipment identifier ID2. The subsets C_(A) ⁽¹⁾ and C_(A) ⁽²⁾ mayintersect, or may not intersect. An association or a mappingrelationship between the foregoing vector or matrix or subset of thematrix with the user equipment identifier may be predefined, or may alsobe notified by the eNB to the UE, for example, notified by using higherlayer signaling, for example, RRC signaling or a downlink controlchannel. Each subset may include only one element. Alternatively, thereference signal set may be associated with a user equipment identifier.For example, the reference signal set notified by the eNB is S, whichincludes in total eight reference signals, namely s1, s2, s3, . . . ,s7, and s8. The foregoing reference signal set is associated with a userequipment identifier ID₀; or the reference signal set received by the UEmay be divided into two or more subsets, and the subsets are associatedwith specific user equipment identifiers separately. For example, thereference signal set received by the UE may be divided into two subsets,one including reference signals s1, s2, s3, and s4 and the other s5, s6,s7, and s8, and then s1, s2, s3, and s4 are associated with identifiersuser equipment ID₁ and ID2. An association or a mapping relationshipbetween the reference signal set and a user equipment identifier may bepredefined, or may also be notified by the eNB.

It should be noted that the user equipment identifier is not necessarilya UE ID in a specific communications protocol, for example, LTE, but mayalso be a specific parameter that is used to distinguish a userequipment attribute, for example, an index or an offset in a user groupor a UE group, or simply an index or an offset used in a same user groupor UE group. The offset or index facilitates implementation ofdistinguishing of attributes related to different beams among userequipment or user groups.

Further, reference signals in the reference signal set may be sent atdifferent times, for example, different subframes, and the differenttimes may be associated with or mapped to different vectors/matrices ordifferent subsets of matrix sets. The different vectors/matrices ordifferent subsets of matrix sets that the reference signals areassociated with or mapped to at different times may be predefined, ormay also be notified by the eNB, for example, notified by using RRCsignaling.

302: The UE selects a precoding matrix based on the first referencesignal set, where the precoding matrix is a function of the userequipment-specific matrix or matrix set.

Specifically, that the precoding matrix is a function of the userequipment-specific matrix or matrix set includes that:

the precoding matrix is a product of two matrices W₁ and W₂, that is,

W=W₁W₂  (29)

where the matrix W₁ is a function of a matrix A or B, and the matrix Aor B is a matrix in the user equipment-specific matrix or matrix set;for example, W₁ is the matrix A or the matrix B;

or

the matrix W₁ is a block diagonal matrix, the block diagonal matrixincludes at least one block matrix, and each block matrix is a functionof the matrix A or B, for example,

W ₁=diag {X ₁ ,X ₂}  (30)

where each block matrix in the matrix W₁ is a function of the matrix Aor the matrix B, for example,

X_(i)=A, i=1,2  (31)

or

X _(i)=diag{ρ₀,ρ₁ , . . . ,}A, i=1,2  (32)

where ρ₀,ρ₁, . . . are scalars, or may also be nonnegative real numbers,or may also be complex numbers, or

X _(i) =C _(i) ⊗D _(i) , i=1,2  (33)

where ⊗ represents a Kronecker product of two matrices, where a k^(th)column of the matrix C_(i) or an l^(th) column d_(l) of D_(i) satisfiesthe following relationship:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m)  (34)

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m)  (35)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }b_(n)  (36)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }b _(n)  (37)

where N_(V), N_(H), N_(C), and N_(D) are all positive integers, a vectora_(m) and a vector b_(n) are an m^(th) column vector of the matrix A andan n^(th) column vector of the matrix B respectively, θ and ϕ are phaseshifts whose values may be 0,π,±π/2,±π/4,±±π/8, and so on.

It should be noted that a value of N_(C) or N_(D) may be infinite, andtherefore 2π/N_(C)=0 or 2π/N_(D)=0, and in this case c_(k)=a_(m),c_(k)=diag{1,1, . . . , 1,e^(jθ),e^(jθ), . . . ,e^(jθ)}a_(m),d_(l)=b_(n), or d_(l)=a_(m), c_(k)=diag{1,1, . . . , 1,e^(jϕ),e^(jϕ), .. . ,e^(jϕ)}b_(n).

At least one of the matrix A or the matrix B is a matrix in the userequipment-specific matrix or matrix set.

In this case, a column vector in the matrix W₂ may have a structurey_(n)=[e_(n) ^(T) e^(jθ) ^(n) e_(n) ^(T)]^(T) where e_(n) represents aselection vector, in which except that an n^(th) element is 1, the restelements are all 0, and θ_(n) is a phase shift. In an example, the blockmatrices X₁ and X₂ each have 4 columns, and the matrix W₂ may berepresented as:

$\begin{matrix}{\mspace{79mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \right\}}} & (38) \\{\mspace{79mu} {{Y \in \left\{ {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{4}} \right\}}\mspace{79mu} {or}}} & (39) \\{\mspace{79mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}}} & (40) \\{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{1}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{4},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{4}} \right)} \right\}} & (41)\end{matrix}$

where {tilde over (e)}_(n), n=1, 2, 3, 4 represents a selection vectorof 4×1, in which except that an n^(th) element of the vector is 1, therest elements of the vector are all 0.

In an example, the block matrices X₁ and X₂ each have 8 columns, and thematrix W₂ may be represented as:

$\begin{matrix}{\mspace{79mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \right\}}} & (42) \\{\mspace{79mu} {{Y \in \left\{ {e_{1},e_{2},e_{3},e_{4},e_{5},e_{6},e_{7},e_{8}} \right\}}\mspace{79mu} {or}}} & (43) \\{\mspace{79mu} {W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}}} & (44) \\{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{2},e_{4}} \right)} \right\}} & (45)\end{matrix}$

where e_(n),n=1, 2, . . . ,8 represents a selection vector of 8×1, inwhich except that an n^(th) element of the vector is 1, the restelements of the vector are all 0.

Alternatively,

The block diagonal matrix W₁ includes only one block matrix, that is,W₁=X , and the block matrix X is a function of the matrix A or B. Forexample, the block matrix X is a Kronecker product of two matrices A andB, that is,

X=A⊗B  (46)

where the matrix A or the matrix B is a matrix in the userequipment-specific (UE-specific) matrix or matrix set;

or,

the block matrix X is a Kronecker product of two matrices C and D ,X=C⊗D. At least one matrix in the two matrices C and D is a function ofthe matrix A or B . For example,

Columns of at least one matrix in the matrices C and D are rotations ofcolumn vectors in the matrix A or B, that is, a k^(th) column vectorc_(k) of the matrix C is:

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2πN) ^(V) ^(/N) ^(C) }a_(m),  (47)

or

c _(k)=diag{1,e ^(j2π/N) ^(C) , . . . ,e ^(j2π(N) ^(V) ^(/2−1)/N) ^(C),e ^(jθ) ,e ^(jθ) e ^(j2π/N) ^(C) , . . . ,e ^(jθ) e ^(j2π(N) ^(V)^(/2−1)/N) ^(C) }a _(m),  (48)

or an l^(th) column vector d_(l) of the matrix D is:

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2πN) ^(H) ^(/N) ^(D) }b_(n),  (49)

or

d _(l)=diag{1,e ^(j2π/N) ^(D) , . . . ,e ^(j2π(N) ^(H) ^(/2−1)/N) ^(D),e ^(jϕ) ,e ^(jϕ) e ^(j2π/N) ^(D) , . . . ,e ^(jϕ) e ^(j2π(N) ^(H)^(/2−1)/N) ^(D) }b _(n)  (50)

where N_(V), N_(H), N_(C), and N_(D) are all positive integers, a vectora_(m) and a vector b_(n) are an m^(th) column vector of the matrix A andan n^(th) column vector of the matrix B respectively, θ and ϕ are phaseshifts whose values may be 0,π,±π/2,±π/4,±±π/8, and so on.

It should be noted that a value of N_(C) or N_(D) may be infinite, andtherefore 2π/N_(C)=0 or 2π/N_(D)=0, and in this case c_(k)=a_(m),c_(k)=diag{1,1, . . . , 1,e^(jθ),e^(jθ), . . . ,e^(jθ)}a_(m),d_(l)=b_(n), or d_(l)=a_(m), c_(k)=diag{1,1, . . . , 1,e^(jϕ),e^(jϕ), .. . ,e^(jϕ)}b_(n).

Optionally, in this case, the matrix W₂ is a column selection matrix,and is used to select r columns from X=C⊗D, where r is a rank of aprecoding matrix. For example, W₂ may be used to always select first rcolumns in X=C⊗D, then

W₂=[e₁ e₂ . . . e_(r)]  (51)

where e_(i) represents a unit column vector, in which except that ani^(th) element is 1, the rest elements are all 0.

Further, vectors c_(k) and d_(k) in the expressions (47) to (50) mayhave granularity finer than that of a_(l) and b_(l), that is,

N_(D)≥N or N_(D)≥N  (52)

303: The UE sends a precoding matrix indicator PMI to the base station,where the PMI corresponds to the selected precoding matrix.

The precoding matrix indicator PMI may include one or more indexes.

Specifically, the precoding matrix indicator PMI may include one index.In this case, the index indicates directly the precoding matrix w. Forexample, there are in total 16 different precoding matrices, and then anindex value n=0, . . . , 15 may be used to indicate the precoding matrixWw having a mark number of 0, 1, . . . 15 respectively.

Alternatively, the precoding matrix indicator PMI may also be twoindexes, for example, i₁ and i₂. W₁ and W₂ in the expression (29) areindicated by using i₁ and i₂ respectively, so that i₁ and i₂ indicatethe precoding matrix w.

Further, the index i₁ may be reported based on a subset of W₁. Forexample, a universal set of W₁ is Q, and subsets of the set Q are Q₀, .. . , and Q₃ separately. In this case, the index i₁ is used to indicatea matrix W₁ in a subset Q_(k), where Q_(k) may be one subset in Q₀, Q₁ .. . , and Q₃. Qk may be predefined, or may be determined and reported bythe UE, or may also be notified by the eNB to the UE. The subsets Q₀, .. . , and Q₃ may not intersect with each other, that is, an intersectionset of the subsets is an empty set; or the subsets Q₀, . . . , and Q₃may intersect with each other, that is, an intersection set of thesubsets is not an empty set.

Alternatively, there may also be three indexes reported by the UE andused to indicate the precoding matrix, for example, i₃, i₄, and is. X₁and X₂ in the expression (30) are implicitly indicated by using i₃ andi₄ respectively, and W₂ is implicitly indicated by using i₅. Therefore,i₃, i₄, and is indicate the precoding matrix w.

Further, the index i3 may be reported based on a subset of X₁. Forexample, a universal set of X₁ is R, and subsets of the set R are R₀, .. . , and R₇ separately. In this case, the index i₃ is used to indicatea matrix X, in a subset R_(k). R_(k) may be one subset in R₀, R₁ . . . ,and R₇. R_(k) may be predefined, or may be determined and reported bythe UE, or may also be notified by the eNB to the UE. The subsets R₀, .. . , and R₇ may not intersect with each other, that is, an intersectionset of the subsets is an empty set; or the subsets R₀, . . . , and R₇may intersect with each other, that is, an intersection set of thesubsets is not an empty set; similarly, i₄ and i₅ may be reported basedon subsets of X₂ and W₂ respectively. The subsets of X₂ and W₂ may bepredefined, or may be determined and reported by the UE, or may also benotified by the eNB to the UE.

Alternatively, indexes reported by the UE and used to indicate theprecoding matrix may also be other three indexes, for example, i₆, i₇and i₈. C_(i) and D_(i) in the expression (33) are implicitly indicatedby using i₆ and i₇ respectively, and w₂ is implicitly indicated by usingi₈. Therefore, i₆, i₇, and is indicate the precoding matrix w, and inthis case, C₁=C₂ and D₁=D₂.

Further, the index i₆ may be reported based on a subset of C. Forexample, a universal set of c_(i) is O, and subsets of the set O are O₀,. . . , and O₇ separately. In this case, the index i₆ is used toindicate a matrix C_(i) in a subset O_(k). O_(k) may be one subset inO₀, O₁ . . . , and O₇. O_(k) may be predefined, or may also bedetermined and reported by the UE, or may also be notified by the eNB tothe UE. The subsets O₀, . . . , and O₇ may not intersect with eachother, that is, an intersection set of the subsets is an empty set; orthe subsets O₀, . . . , O₇ may intersect with each other, that is, anintersection set of the subsets is not an empty set; similarly, i₇ andis may be reported based on subsets of D_(i) and W₂ respectively. Thesubsets of D_(i) and W₂ may be predefined, or may be determined andreported by the UE, or may also be notified by the eNB to the UE.

Specifically, indexes reported by the UE and used to indicate theprecoding matrix may also be four indexes, for example, i₉, i₁₀, i₁₁,and i₁₂. C₁ and C ₂ in the expression (33) are implicitly indicated byusing i₉ and i₁₀ respectively, and D₁=D₂ and W₂ are indicated by usingin and i₁₂ respectively. Therefore, i₉, i₁₀, i₁₁, and i₁₂ indicate theprecoding matrix w.

Further, i₉, i₁₀, i₁₁, and i₁₂ may be reported based on subsets of C₁,C₂, D_(i), and W₂ respectively. The subsets of C₁, C₂, D_(i), and W₂ maybe predefined, or may be determined and reported by the UE, or may alsobe notified by the eNB to the UE.

Specifically, when the UE selects the precoding matrix and determines afirst index based on the first reference signal set, the index value maybe calculated based on one reference signal subset. For example, theforegoing index value n is calculated based on the reference signalsubset P in step 301, or the index values i₁ and i₂, or i₃, i₄, and i₅,or i₆, i₇, and i₈, or i₉, i₁₀, i₁₁, and i₁₂ are calculated based on thereference signal subset P in step 301.

Alternatively, the index value may be calculated in combination based onmultiple reference signal subsets. For example, the index value n iscalculated based on the reference signal subsets P1 and P2 in step 301,or the index values i₁ and i₂, or i₃, i₄, and i₅, or i₆, i₇, and i₈, ori₉, i₁₀, i₁₁, and i₁₂ are calculated based on the reference signalsubsets P1 and P2 in step 301.

Alternatively, the index values are calculated separately based onmultiple reference signal subsets. For example, the index value i₃ iscalculated based on the reference signal subset P1 in step 301, and theindex values i₄ and i₅ are calculated based on the reference signalsubset P2 in step 301. Alternatively, the index value i₆ is calculatedbased on the reference signal subset P1 in step 301, and the indexvalues i₇ and i₈ are calculated based on the reference signal subset P2in step 301. Alternatively, the index values i₉ and i₁₀ are calculatedbased on the reference signal subset P1 in step 301, and the indexvalues i₁₁ and i₁₂ are calculated based on the reference signal subsetP2 in step 301.

Specifically, the UE may determine the foregoing one or more indexesaccording to a measured channel state based on a preset criterion, andthe preset criterion may be a maximum throughput criterion or a maximumcapacity criterion. After the one or more indexes are obtained, the UEmay feed back the indexes to the eNB by using a PUCCH or a PUSCH.

Further, the precoding matrix indicator PMI may include one or moreindexes, and the UE may report the indexes to the eNB through differentsubframes by using a physical uplink control channel (PUCCH).

Further still, the foregoing multiple different indexes may be reportedto the eNB through different subframes for different subbands on afrequency domain.

It should be noted particularly that matrices corresponding to theindexes may be single matrices, so that corresponding indexes do notneed to be fed back. The single matrix may be a predefined matrix, ormay also be notified by a base station by using signaling, or may alsobe obtained implicitly according to other parameters. For example, W₂ isfixedly selected as the matrix shown in the expression (51), so that anindex corresponding to W₂ does not need to be fed back. In this case, W₂is obtained implicitly according to a rank r of the precoding matrix.

304: The base station obtains the precoding matrix w based on thereceived precoding matrix indicator PMI.

305: The base station uses the precoding matrix w to transmit a signalvector s. Specifically, after precoding, a transmitted signal vector isWs.

306: The UE receives the signal sent by the base station and performsdata detection. Specifically, the signal received by the UE is:

y=HWs+n

where y is a received signal vector, H is a channel matrix obtainedthrough estimation, and n is measured noise and interference.

In this way, a first reference signal set is associated with orcorresponds to a user equipment-specific matrix or matrix set, and aprecoding matrix is a function of the user equipment-specific matrix ormatrix set. Therefore, user equipment can select, based on the userequipment-specific matrix or matrix set, the precoding matrix and feedback a PMI, and a set of the precoding matrix forms a userequipment-specific codebook but not a cell specific codebook or systemspecific codebook. The cell specific codebook or system specificcodebook is a precoding matrix set designed for all users in a cell or asystem, while the user equipment-specific codebook is a subset of thecell specific codebook or system specific codebook. Therefore, in thisembodiment of the present invention, CSI feedback precision can beimproved without excessively increasing feedback overhead, therebyimproving system performance.

Besides, a codebook structure W=W₁W₂ is used, where W₁=diag{X₁, X₂} andX_(i)=C_(i)⊗D_(i), i=1, 2 , or W₁=X=C⊗D , quantization in a verticaldirection and a horizontal direction can be effectively supported, anddegrees of freedom at a horizontal and a vertical direction of an activeantenna system AAS is fully utilized, so that feedback precision isimproved, and MIMO performance, especially MU-MIMO performance, isimproved.

Moreover, one or more indexes are fed back based on a subset to indicatea precoding matrix, and correlation between time/frequency domain/spaceof a channel is fully utilized, so that feedback overhead is greatlyreduced.

Further, before step 301 of receiving a first reference signal set sentby a base station, the following optional steps may further be included:

receiving a second reference signal set sent by the base station, wherethe second reference signal set is associated with a subset of a matrixor matrix set; and

determining and reporting, by the UE based on the received secondreference signal set, a second index, where the second index is used forindicating an antenna port or antenna port subset, initially selected bythe UE, in the second reference signal set, or a subset of a matrix ormatrix set that is associated with the antenna port or antenna portsubset initially selected by the UE.

The first reference signal set is a subset of the second referencesignal set, or the second reference signal set is a superset of thefirst reference signal set.

Specifically, that the first reference signal set is a subset of thesecond reference signal set (or equivalently, the second referencesignal set is a superset of the first reference signal set) includesthat: the second reference signal set is the same as the first referencesignal set; or the second reference signal set is a proper subset of thefirst reference signal set, and in this case, a quantity of referencesignals included in the second reference signal set is less than aquantity of reference signals included in the first reference signalset.

Further, the base station uses a reference signal or a reference signalsubset corresponding to the antenna port or antenna port subset,initially selected by the UE and indicated by the second index that isreported by the UE, in the second reference signal set, as the firstreference signal set; or the base station uses a subset of a matrix ormatrix set that is associated with the antenna port or antenna portsubset initially selected by the UE and indicated by the second indexthat is reported by the UE, as a matrix or matrix set that is associatedwith the first reference signal set.

It should be noted that operation based on the second index by the basestation is not limited in this embodiment of the present invention. Inother words, the base station may refer to the second index asassistance, but the base station also may not refer to the second index.

FIG. 4 is a block diagram of user equipment according to an embodimentof the present invention. The user equipment 40 in FIG. 4 includes areceiving unit 41, a determining unit 42, and a sending unit 43.

The receiving unit 41 receives a first reference signal set sent by abase station, where the first reference signal set is associated with auser equipment-specific (UE-specific) matrix or matrix set. Thedetermining unit 42 selects a precoding matrix based on the firstreference signal set, where the precoding matrix is a function of theuser equipment-specific matrix or matrix set. The sending unit 43 sendsa precoding matrix indicator PMI to the base station, where the PMIcorresponds to the selected precoding matrix.

In this embodiment of the present invention, a first reference signalset is associated with or corresponds to a user equipment-specificmatrix or matrix set, a precoding matrix is a function of the userequipment-specific matrix or matrix set, so that the UE can select,based on the user equipment-specific matrix or matrix set, the precodingmatrix and feed back a PMI, and a set of the precoding matrix forms auser equipment-specific codebook but not a cell specific codebook orsystem specific codebook. The cell specific codebook or system specificcodebook is a precoding matrix set designed for all users in a cell or asystem, while the user equipment-specific codebook is a subset of thecell specific codebook or system specific codebook. Therefore, in thisembodiment of the present invention, CSI feedback precision can beimproved without excessively increasing feedback overhead, therebyimproving system performance.

Optionally, as an embodiment, the receiving unit 41 is furtherconfigured to receive the user equipment-specific matrix or matrix setnotified by the base station.

Optionally, as another embodiment, the receiving unit is furtherconfigured to: before the first reference signal set is received,receive a second reference signal set sent by the base station, wherethe second reference signal set is associated with a matrix or matrixset; the determining unit is further configured to determine a secondindex based on the second reference signal set, where the second indexis used for indicating an antenna port or antenna port subset selectedby the user equipment, or a matrix or matrix set that is associated withthe antenna port or antenna port subset selected by the user equipment;and the sending unit is further configured to send the second index tothe base station.

Optionally, the first reference signal set is a subset of the secondreference signal set.

Optionally, the matrix or matrix set associated with the secondreference signal set is cell specific or system specific.

Optionally, as another embodiment, the receiving unit is specificallyconfigured to receive reference signals of the second reference signalset that are sent at different times by the base station. Here,different times may be associated with a same matrix or differentmatrices separately, or may be associated with a same subset ordifferent subsets of a matrix set separately.

Optionally, as another embodiment, the first reference signal setincludes one or more reference signal subsets, and the reference signalsubset corresponds to a co-polarized antenna port subset, or correspondsto an antenna port subset that is arranged in a same direction in anantenna port array, or corresponds to an antenna port subset that islocated at a quasi-co-location.

Optionally, as another embodiment, the receiving unit is specificallyconfigured to receive reference signals of the first reference signalset that are sent at different times by the base station. Here,different times may be associated with a same matrix or differentmatrices separately, or may be associated with a same subset ordifferent subsets of a matrix set separately.

Optionally, as another embodiment, the precoding matrix W is a productof two matrices W₁ and W₂, W=W₁W₂ where the matrix W₁ is a blockdiagonal matrix, the block diagonal matrix includes at least one blockmatrix, and each block matrix is a function of the userequipment-specific matrix or matrix set.

Optionally, the matrix W₂ is used to select or perform weightedcombination on column vectors in the matrix W₁, so as to form the matrixw.

Optionally, as another embodiment, each block matrix X is a Kroneckerproduct of two matrices C and D , X=C⊗D, and at least one matrix in thetwo matrices C and D is a function of the user equipment-specific matrixor matrix set.

Optionally, as another embodiment, columns of at least one matrix in thetwo matrices C and D are rotations of column vectors in a matrix in theuser equipment-specific matrix or matrix set, that is, a k^(th) columnvector c_(k) of the matrix C is shown in the expression (2) or (3); oran l^(th) column vector d_(l) of the matrix D is shown in the expression(4) or (5), where N_(V), N_(H), N_(C), and N_(D) are positive integers,a_(m) is an m^(th) column vector of a matrix A, and the matrix A is amatrix in the user equipment-specific matrix or matrix set.

It should be noted that, that column vectors of the matrix C or matrix Dthat corresponds to the block matrix X at a different location on adiagonal in W₁ satisfy the expressions (2) to (5) does not mean that theblock matrix X at a different location on a diagonal in W₁ has a samematrix C or matrix D. In contrast, the block matrix X at a differentlocation may have a same or different matrix C or matrix D.

Optionally, as another embodiment, a matrix in the userequipment-specific matrix or matrix set is a matrix formed by columnsbeing DFT vectors, or a matrix formed by column vectors of a Hadamardmatrix or a Householder matrix.

Optionally, as another embodiment, the DFT vector a_(l) is shown in theexpression (6), where N_(C)≥N or N_(D)≥N.

Optionally, as another embodiment, the first reference signal setincludes at least one reference signal subset, and the reference signalsubset is associated with a set of the matrix C or the matrix D.

Optionally, as another embodiment, the reference signal subset has asending period longer than that of another reference signal.

FIG. 5 is a block diagram of a base station according to an embodimentof the present invention. The base station 50 in FIG. 5 includes asending unit 51 and a receiving unit 52.

The sending unit 51 is configured to send a first reference signal setto user equipment, where the first reference signal set is associatedwith a user equipment-specific (UE-specific) matrix or matrix set; andthe receiving unit 52 is configured to receive a precoding matrixindicator PMI sent by the user equipment, where the PMI is used forindicating a precoding matrix that is selected based on the firstreference signal by the user equipment, and the precoding matrix is afunction of the user equipment-specific matrix or matrix set.

In this embodiment of the present invention, a first reference signalset is associated with or corresponds to a user equipment-specificmatrix or matrix set, a precoding matrix is a function of the userequipment-specific matrix or matrix set, so that user equipment canselect, based on the matrix or matrix set, the precoding matrix and feedback a PMI, and a set of the precoding matrix forms a userequipment-specific codebook but not a cell specific codebook or systemspecific codebook. The cell specific codebook or system specificcodebook is a precoding matrix set designed for all users in a cell or asystem, while the user equipment-specific codebook is a subset of thecell specific codebook or system specific codebook. Therefore, in thisembodiment of the present invention, CSI feedback precision can beimproved without excessively increasing feedback overhead, therebyimproving system performance.

Optionally, the base station 50 may further include an acquiring unit53, configured to obtain the precoding matrix according to the receivedPMI.

Optionally, as an embodiment, the sending unit 51 is further configuredto notify the user equipment of the user equipment-specific matrix ormatrix set.

Optionally, as another embodiment, the sending unit 51 is furtherconfigured to: before the first reference signal set is sent to the userequipment, send a second reference signal set to the user equipment,where the second reference signal set is associated with a matrix ormatrix set; and the receiving unit is further configured to receive asecond index that is determined based on the second reference signal setby the user equipment, where the second index is used for indicating anantenna port or antenna port subset selected by the user equipment, or amatrix or matrix set that is associated with the antenna port or antennaport subset selected by the user equipment.

Optionally, the first reference signal set is a subset of the secondreference signal set.

Optionally, the matrix or matrix set associated with the secondreference signal set is cell specific or system specific.

Optionally, as an embodiment, the acquiring unit 53 is furtherconfigured to measure an uplink physical channel or an uplink physicalsignal, and obtain channel estimation of the user equipment according tochannel reciprocity. Based on a predefined criterion, the firstreference signal and the user equipment-specific matrix or matrix setare selected for a user. The uplink physical channel may be a physicaluplink control channel (PUCCH) or a physical uplink shared channel(PUSCH); the physical signal may be a sounding reference signal (SRS) oranother uplink demodulation reference signal (DMRS).

Optionally, as another embodiment, the sending unit is specificallyconfigured to send reference signals of the second reference signal setto the user equipment at different times. Here, different times may beassociated with a same matrix or different matrices separately, or maybe associated with a same subset or different subsets of a matrix setseparately.

Optionally, as another embodiment, the first reference signal setincludes one or more reference signal subsets, and the reference signalsubset corresponds to a co-polarized antenna port subset, or correspondsto an antenna port subset that is arranged in a same direction in anantenna port array, or corresponds to a quasi-co-location antenna portsubset.

Optionally, as another embodiment, the sending unit is specificallyconfigured to send reference signals of the first reference signal setto the user equipment at different times. Here, different times may beassociated with a same matrix or different matrices separately, or maybe associated with a same subset or different subsets of a matrix setseparately.

Optionally, as another embodiment, the precoding matrix w is a productof two matrices W₁ and W₂ , W=W₁W₂ where the matrix W₁ is a blockdiagonal matrix, the block diagonal matrix includes at least one blockmatrix, and each block matrix is a function of the userequipment-specific matrix or matrix set.

Optionally, the matrix W₂ is used to select or perform weightedcombination on column vectors in the matrix W₁, so as to form the matrixw.

Optionally, as another embodiment, each block matrix X is a Kroneckerproduct of two matrices C and D, X=C⊗D, and at least one matrix in thetwo matrices C and D is a function of the user equipment-specific matrixor matrix set.

Optionally, as another embodiment, columns of at least one matrix in thetwo matrices C and D are rotations of column vectors in a matrix in theuser equipment-specific matrix or matrix set, that is, a k^(th) columnvector c_(k) of the matrix C is shown in the expression (2) or (3); oran l^(th) column vector d_(l) of the matrix D is shown in the expression(4) or (5), where N_(V), N_(H), N_(C), and N_(D) are positive integers,a_(m) is an m^(th) column vector of a matrix A, and the matrix A is amatrix in the user equipment-specific matrix or matrix set.

It should be noted that, that column vectors of the matrix C or matrix Dthat corresponds to the block matrix X at a different location on adiagonal in W₁ satisfy the expressions (2) to (5) does not mean that theblock matrix X at a different location on a diagonal in W₁ has a samematrix C or matrix D. In contrast, the block matrix X at a differentlocation may have a same or different matrix C or matrix D.

Optionally, as another embodiment, a matrix in the userequipment-specific matrix or matrix set is a matrix formed by columnsbeing DFT vectors, or a matrix formed by column vectors of a Hadamardmatrix or a Householder matrix.

Optionally, as another embodiment, the DFT vector a_(l) is shown in theexpression (6), where N_(C)≥N or N_(D)≥N.

Optionally, as another embodiment, the first reference signal setincludes at least one reference signal subset, and the reference signalsubset is associated with a set of the matrix C or the matrix D.

Optionally, as another embodiment, the reference signal subset has asending period longer than that of another reference signal.

FIG. 6 is a block diagram of user equipment according to anotherembodiment of the present invention. The user equipment 60 in FIG. 6includes a receiver 62, a transmitter 63, a processor 64, and a memory65.

The receiver 62 is configured to receive a first reference signal setsent by a base station, where the first reference signal set isassociated with a user equipment-specific (UE specific) matrix or matrixset.

The memory 65 stores an instruction that enables the processor 64 toperform the following operation: selecting a precoding matrix based onthe first reference signal set, where the precoding matrix is a functionof the user equipment-specific matrix or matrix set.

The transmitter 63 is configured to send a precoding matrix indicatorPMI to the base station, where the PMI corresponds to the selectedprecoding matrix.

In this embodiment of the present invention, a first reference signalset is associated with or corresponds to a user equipment-specificmatrix or matrix set, a precoding matrix is a function of the userequipment-specific matrix or matrix set, so that the user equipment canselect, based on the user equipment-specific matrix or matrix set, theprecoding matrix and feed back a PMI, and a set of the precoding matrixforms a user equipment-specific codebook but not a cell specificcodebook or system specific codebook. The cell specific codebook orsystem specific codebook is a precoding matrix set designed for allusers in a cell or a system, while the user equipment-specific codebookis a subset of the cell specific codebook or system specific codebook.Therefore, in this embodiment of the present invention, CSI feedbackprecision can be improved without excessively increasing feedbackoverhead, thereby improving system performance.

The receiver 62, the transmitter 63, the processor 64, and the memory 65may be integrated into a processing chip. Alternatively, as shown inFIG. 6, the receiver 62, the transmitter 63, the processor 64, and thememory 65 are connected by using a bus system 66.

In addition, the user equipment 60 may further include an antenna 61.The processor 64 may further control an operation of the user equipment60, and the processor 64 may further be referred to as a CPU (centralprocessing unit). The memory 65 may include a read only memory and arandom access memory, and provides instructions and data to theprocessor 64. A part of the memory 65 may further include a non-volatilerandom access memory. Components of the user equipment 60 are coupledtogether by using a bus system 66. The bus system 66 may include, inaddition to a data bus, a power bus, a control bus, a status signal bus,and the like. However, for the purpose of clear description, all busesare marked as the bus system 66 in the figure.

Optionally, as an embodiment, the receiver 62 is further configured toreceive the user equipment-specific matrix or matrix set notified by thebase station.

Optionally, as another embodiment, the receiver 62 is further configuredto: before the first reference signal set is received, receive a secondreference signal set sent by the base station, where the secondreference signal set is associated with a matrix or matrix set; thememory 65 further stores an instruction that enables the processor 64 toperform the following operation: determining a second index based on thesecond reference signal set, where the second index is used forindicating an antenna port or antenna port subset selected by the userequipment, or a matrix or matrix set that is associated with the antennaport or antenna port subset selected by the user equipment 60; and thetransmitter 63 is further configured to send the second index to thebase station.

Optionally, the first reference signal set is a subset of the secondreference signal set.

Optionally, as another embodiment, the receiver 62 is specificallyconfigured to receive reference signals of the second reference signalset that are sent at different times by the base station. Here,different times may be associated with a same matrix or differentmatrices separately, or may be associated with a same subset ordifferent subsets of a matrix set separately.

Optionally, as another embodiment, the first reference signal setincludes one or more reference signal subsets, and the reference signalsubset corresponds to a co-polarized antenna port subset, or correspondsto an antenna port subset that is arranged in a same direction in anantenna port array, or corresponds to an antenna port subset that islocated at a quasi-co-location.

Optionally, as another embodiment, the receiver 62 is specificallyconfigured to receive reference signals of the first reference signalset that are sent at different times by the base station. Here,different times may be associated with a same matrix or differentmatrices separately, or may be associated with a same subset ordifferent subsets of a matrix set separately.

Optionally, as another embodiment, the precoding matrix w is a productof two matrices W₁ and W₂, W=W₁W₂, where the matrix W₁ is a blockdiagonal matrix, the block diagonal matrix includes at least one blockmatrix, and each block matrix is a function of the userequipment-specific matrix or matrix set.

Optionally, the matrix W₂ is used to select or perform weightedcombination on column vectors in the matrix W₁, so as to form the matrixw.

Optionally, as another embodiment, each block matrix X is a Kroneckerproduct of two matrices C and D, X=C⊗D, and at least one matrix in thetwo matrices C and D is a function of the user equipment-specific matrixor matrix set.

Optionally, as another embodiment, columns of at least one matrix in thetwo matrices C and D are rotations of column vectors in a matrix in theuser equipment-specific matrix or matrix set, that is, a k^(th) columnvector c_(k) of the matrix C is shown in the expression (2) or (3); oran l^(th) column vector d_(l) of the matrix D is shown in the expression(4) or (5), where N_(V), N_(H), N_(C), and N_(D) are positive integers,a_(m) is an m^(th) column vector of a matrix A, and the matrix A is amatrix in the user equipment-specific matrix or matrix set.

It should be noted that, that column vectors of the matrix C or matrix Dthat corresponds to the block matrix X at a different location on adiagonal in W₁ satisfy the expressions (2) to (5) does not mean that theblock matrix X at a different location on a diagonal in W₁ has a samematrix C or matrix D. In contrast, the block matrix X at a differentlocation may have a same or different matrix C or matrix D.

Optionally, as another embodiment, a matrix in a subset of the userequipment-specific matrix or matrix set is a matrix formed by columnsbeing DFT vectors, or a matrix formed by column vectors of a Hadamardmatrix or a Householder matrix.

Optionally, as another embodiment, the DFT vector a_(l) is shown in theexpression (6), where N_(C)≥N or N_(D)≥N.

FIG. 7 is a block diagram of a base station according to anotherembodiment of the present invention. The base station 70 in FIG. 7includes a transmitter 72, a receiver 73, a processor 74, and a memory75.

The transmitter 72 is configured to send a first reference signal set touser equipment, where the first reference signal set is associated witha user equipment-specific (UE specific) matrix or matrix set.

The receiver 73 is configured to receive a precoding matrix indicatorPMI sent by the user equipment, where the PMI is used for indicating aprecoding matrix that is selected based on the first reference signal bythe user equipment, and the precoding matrix is a function of the userequipment-specific matrix or matrix set.

Optionally, the memory 75 may store an instruction that enables theprocessor 74 to perform the following operation: obtaining the precodingmatrix according to the received PMI.

In this embodiment of the present invention, a first reference signalset is associated with or corresponds to a user equipment-specificmatrix or matrix set, a precoding matrix is a function of the userequipment-specific matrix or matrix set, so that user equipment canselect, based on the user equipment-specific matrix or matrix set, theprecoding matrix and feed back a PMI, and a set of the precoding matrixforms a user equipment-specific codebook but not a cell specificcodebook or system specific codebook. The cell specific codebook orsystem specific codebook is a precoding matrix set designed for allusers in a cell or a system, while the user equipment-specific codebookis a subset of the cell specific codebook or system specific codebook.Therefore, in this embodiment of the present invention, CSI feedbackprecision can be improved without excessively increasing feedbackoverhead, thereby improving system performance.

The transmitter 72, the receiver 73, the processor 74, and the memory 75may be integrated into a processing chip. Alternatively, as shown inFIG. 7, the transmitter 72, the receiver 73, the processor 74, and thememory 75 are connected by using a bus system 76.

In addition, the base station 70 may further include an antenna 71. Theprocessor 74 may further control an operation of the base station 70,and the processor 74 may further be referred to as a CPU (centralprocessing unit). The memory 75 may include a read only memory and arandom access memory, and provides instructions and data to theprocessor 74. A part of the memory 75 may further include a non-volatilerandom access memory. Components of the base station 70 are coupledtogether by using a bus system 76. The bus system 76 may include, inaddition to a data bus, a power bus, a control bus, a status signal bus,and the like. However, for the purpose of clear description, all busesare marked as the bus system 76 in the figure.

Optionally, as an embodiment, the transmitter 72 is further configuredto notify the user equipment of the user equipment-specific matrix ormatrix set.

Optionally, as another embodiment, the transmitter 72 is furtherconfigured to: before the first reference signal set is sent to the userequipment, send a second reference signal set to the user equipment,where the second reference signal set is associated with a matrix ormatrix set; and the receiver 73 is further configured to receive asecond index that is determined based on the second reference signal setby the user equipment, where the second index is used for indicating anantenna port or antenna port subset selected by the user equipment, or amatrix or matrix set that is associated with the antenna port or antennaport subset selected by the user equipment.

Optionally, the first reference signal set is a subset of the secondreference signal set.

Optionally, the matrix or matrix set associated with the secondreference signal set is cell specific or system specific.

Optionally, as an embodiment, the processor is further configured tomeasure an uplink physical channel or an uplink physical signal, andobtain channel estimation of the user equipment according to channelreciprocity. Based on a predefined criterion, the first reference signaland the user equipment-specific matrix or matrix set are selected for auser. The uplink physical channel may be a physical uplink controlchannel (PUCCH) or a physical uplink shared channel (PUSCH); thephysical signal may be a sounding reference signal (SRS) or anotheruplink demodulation reference signal (DMRS).

Optionally, as another embodiment, the transmitter 72 is specificallyconfigured to send reference signals of the second reference signal setto the user equipment at different times. Here, different times may beassociated with a same matrix or different matrices separately, or maybe associated with a same subset or different subsets of a matrix setseparately.

Optionally, as another embodiment, the first reference signal setincludes one or more reference signal subsets, and the reference signalsubset corresponds to a co-polarized antenna port subset, or correspondsto an antenna port subset that is arranged in a same direction in anantenna port array, or corresponds to a quasi-co-location antenna portsubset.

Optionally, as another embodiment, the transmitter 72 is specificallyconfigured to send reference signals of the first reference signal setto the user equipment at different times. Here, different times may beassociated with a same matrix or different matrices separately, or maybe associated with a same subset or different subsets of a matrix setseparately.

Optionally, as another embodiment, the precoding matrix w is a productof two matrices W₁ and W₂, W=W₁W₂ where the matrix W₁ is a blockdiagonal matrix, the block diagonal matrix includes at least one blockmatrix, and each block matrix is a function of the userequipment-specific matrix or matrix set.

Optionally, the matrix W₂ is used to select or perform weightedcombination on column vectors in the matrix W₁, so as to form the matrixw.

Optionally, as another embodiment, each block matrix X is a Kroneckerproduct of two matrices C and D, X=C⊗D, and at least one matrix in thetwo matrices C and D is a function of the user equipment-specific matrixor matrix set.

Optionally, as another embodiment, columns of at least one matrix in thetwo matrices C and D are rotations of column vectors in a matrix in theuser equipment-specific matrix or matrix set, that is, a k^(th) columnvector C of the matrix c_(k) is shown in the expression (2) or (3); oran l^(th) column vector ^(d)1 of the matrix D is shown in the expression(4) or (5), where N_(V), N_(H), N_(C), and N_(D) are positive integers,a_(m) is an m^(th) column vector of a matrix A, and the matrix A is amatrix in the user equipment-specific matrix or matrix set.

It should be noted that, that column vectors of the matrix C or matrix Dthat corresponds to the block matrix X at a different location on adiagonal in W₁ satisfy the expressions (2) to (5) does not mean that theblock matrix X at a different location on a diagonal in W₁ has a samematrix C or matrix D. In contrast, the block matrix X at a differentlocation may have a same or different matrix C or matrix D.

Optionally, as another embodiment, a matrix in the userequipment-specific matrix or matrix set is a matrix formed by columnsbeing DFT vectors, or a matrix formed by column vectors of a Hadamardmatrix or a Householder matrix.

Optionally, as another embodiment, the DFT vector a_(l) is shown in theexpression (6), where N_(C)≥N or N_(D)≥N.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of the present invention.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein again.

In the several embodiments provided in the present application, itshould be understood that the disclosed system, apparatus, and methodmay be implemented in other manners. For example, the describedapparatus embodiment is merely exemplary. For example, the unit divisionis merely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual needs to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of the presentinvention may be integrated into one processing unit, or each of theunits may exist alone physically, or two or more units may be integratedinto one unit.

When the functions are implemented in the form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of the present inventionessentially, or the part contributing to the prior art, or some of thetechnical solutions may be implemented in a form of a software product.The computer software product is stored in a storage medium, andincludes several instructions for instructing a computer device (whichmay be a personal computer, a server, or a network device) to performall or some of the steps of the methods described in the embodiments ofthe present invention. The foregoing storage medium includes: any mediumthat can store program code, such as a USB flash drive, a removable harddisk, a read-only memory (ROM), a random access memory (RAM), a magneticdisk, or an optical disc.

The foregoing descriptions are merely specific implementation manners ofthe present invention, but are not intended to limit the protectionscope of the present invention. Any variation or replacement readilyfigured out by a person skilled in the art within the technical scopedisclosed in the present invention shall fall within the protectionscope of the present invention. Therefore, the protection scope of thepresent invention shall be subject to the protection scope of theclaims.

What is claimed is:
 1. A method for determining a precoding matrixindicator, performed by a base station, comprising: sending a firstreference signal set to user equipment, wherein the first referencesignal set is associated with a user equipment-specific matrix set,wherein each matrix in the user equipment-specific matrix set comprisesat least one column, and wherein each column comprises at least tworows; and receiving a precoding matrix indicator (PMI) sent by the userequipment, wherein the PMI is used for indicating a precoding matrix Wthat is selected based on the first reference signal set by the userequipment, wherein the precoding matrix W is a product of two matricesW₁ and W₂, wherein W=W₁W₂, wherein the matrix W₁ is a block diagonalmatrix, wherein the block diagonal matrix comprises two block matrices,wherein each block matrix X of the two block matrices is a Kroneckerproduct of two matrices C and D, wherein X=C⊗D, wherein the matrix C andthe matrix D are respectively a function of matrix A and matrix B in theuser equipment-specific matrix set, wherein each of the matrix W₂, thematrix C, and the matrix D comprises at least one column, and whereineach column comprises at least two rows.
 2. The method according toclaim 1, wherein: each column in the matrix C is a column in the matrixA; and each column in the matrix D is a column in the matrix B.
 3. Themethod according to claim 1, wherein the matrix A is a matrix whosecolumns are discrete Fourier Transformation (DFT) vectors, wherein thematrix C is not equal to the matrix A, wherein the matrix B is a matrixwhose columns are DFT vectors, and wherein the matrix D is not equal tothe matrix B.
 4. The method according to claim 1, wherein the matrix W₂is used for selecting a column vector or weighted combination of columnvectors in the matrix W₁ to form the precoding matrix W.
 5. The methodaccording to claim 1, wherein the user equipment-specific matrix set isnotified by the base station.
 6. The method according to claim 1,wherein the first reference signal set comprises at least two referencesignal subsets, and wherein each of the at least two reference signalsubsets corresponds to one of the following: a subset of co-polarizedantenna ports; a subset of antenna ports that are arranged in a samedirection in an antenna port array; and a subset of antenna ports thatare quasi-co-located.
 7. The method according to claim 1, wherein thePMI comprises three indexes i₆, i₇ and i₈, wherein the index i₆indicates the matrix C, wherein the index i₇ indicates the matrix D, andwherein the index i₈ indicates the matrix W₂.
 8. The method according toclaim 1, one of: wherein the matrix C is used for quantization ofhorizontal direction of an antenna system, and the matrix D is used forquantization of vertical direction of an antenna system, or wherein thematrix C is used for quantization of vertical direction of an antennasystem, and the matrix D is used for quantization of horizontaldirection of an antenna system.
 9. A base station, comprising: a memorycomprising instructions; and at least one processor in communicationwith the memory, wherein the at least one processor executes theinstructions to: send a first reference signal set to user equipment,wherein the first reference signal set is associated with a userequipment-specific matrix set, wherein each matrix in the userequipment-specific matrix set comprises at least one column, and whereineach column comprises at least two rows; and receive a precoding matrixindicator (PMI) sent by the user equipment, wherein the PMI is used forindicating a precoding matrix W that is selected based on the firstreference signal set by the user equipment, wherein the precoding matrixW is a product of two matrices W₁ and W₂, wherein W=W₁W₂, wherein thematrix W₁ is a block diagonal matrix, wherein the block diagonal matrixcomprises two block matrices, wherein each block matrix X of the twoblock matrices is a Kronecker product of two matrices C and D, whereinX=C⊗D, wherein the matrix C and the matrix D are respectively a functionof matrix A and matrix B in the user equipment-specific matrix set,wherein each of the matrix W₂, the matrix C, and the matrix D comprisesat least one column, and wherein each column comprises at least tworows.
 10. The base station according to claim 9, wherein: each column inthe matrix C is a column in the matrix A; and each column in the matrixD is a column in the matrix B.
 11. The base station according to claim9, wherein the matrix A is a matrix whose columns are discrete FourierTransformation (DFT) vectors, wherein the matrix C is not equal to thematrix A, wherein the matrix B is a matrix whose columns are DFTvectors, and wherein the matrix D is not equal to the matrix B.
 12. Thebase station according to claim 9, wherein the matrix W₂ is used forselecting a column vector or weighted combination of column vectors inthe matrix W₁ to form the precoding matrix W.
 13. The base stationaccording to claim 9, wherein the user equipment-specific matrix set isnotified by the base station.
 14. The base station according to claim 9,wherein the first reference signal set comprises at least two referencesignal subsets, and wherein each of the at least two reference signalsubsets corresponds to one of the following: a subset of co-polarizedantenna ports; a subset of antenna ports that are arranged in a samedirection in an antenna port array; and a subset of antenna ports thatare quasi-co-located.
 15. The base station according to claim 9, whereinthe PMI comprises three indexes i₆, i₇, and i₈, wherein the index i₆indicates the matrix C, wherein the index i₇ indicates the matrix D, andwherein the index i₈ indicates the matrix W₂.
 16. The base stationaccording to claim 9, one of: wherein the matrix C is used forquantization of horizontal direction of an antenna system, and thematrix D is used for quantization of vertical direction of an antennasystem, or wherein the matrix C is used for quantization of verticaldirection of an antenna system, and the matrix D is used forquantization of horizontal direction of an antenna system.
 17. A basestation, comprising: a transmitter, the transmitter configured to send afirst reference signal set to user equipment, wherein the firstreference signal set is associated with a user equipment-specific matrixset, wherein each matrix in the user equipment-specific matrix setcomprises at least one column, and wherein each column comprises atleast two rows; and a receiver, the receiver configured to receive aprecoding matrix indicator (PMI) sent by the user equipment, wherein thePMI is used for indicating a precoding matrix W that is selected basedon the first reference signal set by the user equipment, wherein theprecoding matrix W is a product of two matrices W₁ and W₂, whereinW=W₁W₂, wherein the matrix W₁ is a block diagonal matrix, wherein theblock diagonal matrix comprises two block matrices, wherein each blockmatrix X of the two block matrices is a Kronecker product of twomatrices C and D, wherein X=C⊗D, wherein the matrix C and the matrix Dare respectively a function of matrix A and matrix B in the userequipment-specific matrix set, wherein each of the matrix W₂, the matrixC, and the matrix D comprises at least one column, and wherein eachcolumn comprises at least two rows.
 18. The base station according toclaim 17, wherein: each column in the matrix C is a column in the matrixA; and each column in the matrix D is a column in the matrix B.
 19. Thebase station according to claim 17, wherein the matrix A is a matrixwhose columns are discrete Fourier Transformation (DFT) vectors, whereinthe matrix C is not equal to the matrix A, wherein the matrix B is amatrix whose columns are DFT vectors, and wherein the matrix D is notequal to the matrix B.
 20. The base station according to claim 17,wherein the matrix W₂ is used for selecting a column vector or weightedcombination of column vectors in the matrix W₁ to form the precodingmatrix W.
 21. The base station according to claim 17, wherein the userequipment-specific matrix set is notified by the base station.
 22. Thebase station according to claim 17, wherein the first reference signalset comprises at least two reference signal subsets, and wherein each ofthe at least two reference signal subsets corresponds to one of thefollowing: a subset of co-polarized antenna ports; a subset of antennaports that are arranged in a same direction in an antenna port array;and a subset of antenna ports that are quasi-co-located.
 23. The basestation according to claim 17, wherein the PMI comprises three indexesi₆, i₇, and i₈, wherein the index i₆ indicates the matrix C, wherein theindex i₇ indicates the matrix D, and wherein the index i₈ indicates thematrix W₂.
 24. The base station according to claim 17, one of: whereinthe matrix C is used for quantization of horizontal direction of anantenna system, and the matrix D is used for quantization of verticaldirection of an antenna system, or wherein the matrix C is used forquantization of vertical direction of an antenna system, and the matrixD is used for quantization of horizontal direction of an antenna system.25. A non-transitory computer-readable storage medium storing computerinstructions which, when executed by one or more processors, cause theone or more processors to perform operations comprising: sending a firstreference signal set to user equipment, wherein the first referencesignal set is associated with a user equipment-specific matrix set,wherein each matrix in the user equipment-specific matrix set comprisesat least one column, and wherein each column comprises at least tworows; and receiving a precoding matrix indicator (PMI) sent by the userequipment, wherein the PMI is used for indicating a precoding matrix Wthat is selected based on the first reference signal set by the userequipment, wherein the precoding matrix W is a product of two matricesW₁ and W₂, wherein W=W₁W₂, wherein the matrix W₁ is a block diagonalmatrix, wherein the block diagonal matrix comprises two block matrices,wherein each block matrix X of the two block matrices is a Kroneckerproduct of two matrices C and D, wherein X=C⊗D, wherein the matrix C andthe matrix D are respectively a function of matrix A and matrix B in theuser equipment-specific matrix set, wherein each of the matrix W₂, thematrix C, and the matrix D comprises at least one column, and whereineach column comprises at least two rows.
 26. The non-transitorycomputer-readable storage medium according to claim 25, wherein eachcolumn in the matrix C is a column in the matrix A, and wherein eachcolumn in the matrix D is a column in the matrix B.
 27. Thenon-transitory computer-readable storage medium according to claim 25,wherein the matrix A is a matrix whose columns are discrete FourierTransformation (DFT) vectors, wherein the matrix C is not equal to thematrix A, wherein the matrix B is a matrix whose columns are DFTvectors, and wherein the matrix D is not equal to the matrix B.
 28. Thenon-transitory computer-readable storage medium according to claim 25,wherein the matrix W₂ is used for selecting a column vector or weightedcombination of column vectors in the matrix W₁ to form the precodingmatrix W.
 29. The non-transitory computer-readable storage mediumaccording to claim 25, wherein the user equipment-specific matrix set isnotified by a base station.
 30. The non-transitory computer-readablestorage medium according to claim 25, wherein the first reference signalset comprises at least two reference signal subsets, and wherein each ofthe at least two reference signal subsets corresponds to one of thefollowing: a subset of co-polarized antenna ports; a subset of antennaports that are arranged in a same direction in an antenna port array;and a subset of antenna ports that are quasi-co-located.
 31. Thenon-transitory computer-readable storage medium according to claim 25,wherein the PMI comprises three indexes i₆, i₇, and i₈, wherein theindex i₆ indicates the matrix C, wherein the index i7 indicates thematrix D, and wherein the index i₈ indicates the matrix W₂.
 32. Thenon-transitory computer-readable storage medium according to claim 25,one of: wherein the matrix C is used for quantization of horizontaldirection of an antenna system, and the matrix D is used forquantization of vertical direction of an antenna system, or wherein thematrix C is used for quantization of vertical direction of an antennasystem, and the matrix D is used for quantization of horizontaldirection of an antenna system.